CG diffuse shader

Here's my CG terrain shader:

 Shader "Custom/Terrain" {
 Properties {
     _Splat0 ("Layer 1 (R)", 2D) = "white" {}
     _Splat1 ("Layer 2 (G)", 2D) = "white" {}
     _Splat2 ("Layer 3 (B)", 2D) = "white" {}
     _Splat3 ("Layer 4 (A)", 2D) = "white" {}
     _Control ("Control (RGBA)", 2D) = "white" {}
     _MainTex ("Never Used", 2D) = "white" {}
 } 
 
 SubShader {
     Tags {
         "SplatCount" = "4"
         "Queue" = "Geometry-100"
         "RenderType" = "Opaque"
     }
         Pass {
             ZTest LEqual
             Lighting on
             ZWrite on
         
             CGPROGRAM
 // Upgrade NOTE: excluded shader from DX11 and Xbox360; has structs without semantics (struct v2f members lightDirection)
 #pragma exclude_renderers d3d11 xbox360
             #pragma vertex vert
             #pragma fragment frag
 
             #include "UnityCG.cginc"
             
             sampler2D_half _Splat0;
             sampler2D_half _Splat1;
             sampler2D_half _Splat2;
             sampler2D_half _Splat3;
             sampler2D_half _Control;
             half4 _Splat0_ST;
             half4 _Splat1_ST;
             half4 _Splat2_ST;
             half4 _Splat3_ST;
             half4 _Control_ST;

             struct a2v
             {
                 half4 vertex : POSITION;
                 half3 normal : NORMAL;
                 half4 texcoord : TEXCOORD0;
             };
             
             struct v2f
             {
                 fixed4 pos : SV_POSITION;
                 half2 uv  : TEXCOORD0;
                 half2 uv0  : TEXCOORD1;
                 half2 uv1  : TEXCOORD2;
                 half2 uv2  : TEXCOORD3;
                 half2 uv3  : TEXCOORD4;
                 fixed4 light : TEXCOORD5;
             };
 
             v2f vert (a2v v)
             {
                 v2f o;
                 o.pos = mul( UNITY_MATRIX_MVP, v.vertex);
                 o.uv = TRANSFORM_TEX (v.texcoord, _Control); 
                 o.uv0 = TRANSFORM_TEX (v.texcoord, _Splat0); 
                 o.uv1 = TRANSFORM_TEX (v.texcoord, _Splat1); 
                 o.uv2 = TRANSFORM_TEX (v.texcoord, _Splat2); 
                 o.uv3 = TRANSFORM_TEX (v.texcoord, _Splat3); 
                 fixed3 toLight = normalize(unity_LightPosition[0].xyz);
                  fixed3 lightColor = saturate(
                                     UNITY_LIGHTMODEL_AMBIENT.rgb
                                             + (unity_LightColor[0].rgb * 
                                             (dot( normalize( mul( (float3x3) UNITY_MATRIX_IT_MV, v.normal)), toLight.xyz ))));


                 o.light = fixed4(lightColor * 2,1) ;


                 return o;
             }
             
             fixed4 frag(v2f i) : COLOR
             {
                 fixed4 c = tex2D (_Control, i.uv);
                 fixed3 c1 = tex2D (_Splat0, i.uv0);
                 fixed3 c2 = tex2D (_Splat1, i.uv1);
                 fixed3 c3 = tex2D (_Splat2, i.uv2);
                 fixed3 c4 = tex2D (_Splat3, i.uv3);
                 return fixed4(((c1.rgb * c.r) + (c2.rgb * c.g) + (c3.rgb * c.b) + (c4.rgb * c.a)), 1) * i.light;
             }
             ENDCG
         }
     } 
     FallBack "Diffuse"
 }