TextureConverterShader: Write EFB2Tex XFB copies with alpha value of 1

This way we don't end up with artifacts of the EFB's alpha values in
frame dumps. XFB copies loaded from RAM also set the alpha to 1, so this
will match.

Source/Core/VideoCommon/TextureConverterShaderGen.cpp

@@ -268,8 +268,8 @@ ShaderCode GenerateShader(APIType api_type, const UidData* uid_data)
       break;
 
     case EFBCopyFormat::XFB:
-      out.Write("  ocol0 = float4(pow(texcol.rgb, float3(gamma_rcp, gamma_rcp, gamma_rcp)), "
-                "texcol.a);\n");
+      out.Write(
+          "  ocol0 = float4(pow(texcol.rgb, float3(gamma_rcp, gamma_rcp, gamma_rcp)), 1.0f);\n");
       break;
 
     default: