Fix post processing shaders crashing on Intel GPUs (#6890)

src/video_core/renderer_opengl/post_processing_opengl.cpp

@@ -41,9 +41,9 @@ constexpr char dolphin_shader_header[] = R"(
 #define lerp mix
 
 // Output variable
-out float4 color;
+layout (location = 0) out float4 color;
 // Input coordinates
-in float2 frag_tex_coord;
+layout (location = 0) in float2 frag_tex_coord;
 // Resolution
 uniform float4 i_resolution;
 uniform float4 o_resolution;