SSR: fixed GLES shader compile warning

Author: TheMostDiligent

Shaders/PostProcess/ScreenSpaceReflection/private/SSR_ComputeStencilMaskAndExtractRoughness.fx

@@ -12,7 +12,13 @@ Texture2D<float>  g_TextureDepth;
 
 float LoadRoughness(int2 PixelCoord)
 {
-    float Roughness = g_TextureMaterialParameters.Load(int3(PixelCoord, 0))[g_SSRAttribs.RoughnessChannel];
+    float4 MaterialParams = g_TextureMaterialParameters.Load(int3(PixelCoord, 0));
+    float4 RoughnessSelector = float4(
+        g_SSRAttribs.RoughnessChannel == 0u ? 1.0 : 0.0,
+        g_SSRAttribs.RoughnessChannel == 1u ? 1.0 : 0.0,
+        g_SSRAttribs.RoughnessChannel == 2u ? 1.0 : 0.0,
+        g_SSRAttribs.RoughnessChannel == 3u ? 1.0 : 0.0);
+    float Roughness = dot(MaterialParams, RoughnessSelector);
     if (!g_SSRAttribs.IsRoughnessPerceptual)
         Roughness = sqrt(Roughness);
     return Roughness;