rsx: Fixup for surface_target_a flag being broken

- While the mask for surface_a is at index 0, the surface cache expects the order to be maintained correctly!
  Set the correct mask since surface store now checks each RTT individually

rpcs3/Emu/RSX/Common/surface_store.h

@@ -887,6 +887,7 @@ namespace rsx
 			if (write_tag == cache_tag && m_skip_write_updates)
 			{
 				// Nothing to do
+				verify(HERE), !m_invalidate_on_write;
 				return;
 			}
 

rpcs3/Emu/RSX/RSXThread.cpp

@@ -1092,7 +1092,8 @@ namespace rsx
 		{
 			if (rsx::method_registers.color_write_enabled(i))
 			{
-				layout.color_write_enabled[i] = true;
+				const auto real_index = mrt_buffers[i];
+				layout.color_write_enabled[real_index] = true;
 				color_write_enabled = true;
 			}
 		}