gfx: Use simpler equality test for IPPU.FrameCount

As it's only incremented here and then reset to 0, avoids integer
division, which can be be expensive on CPUs without this instruction
such as pre-ARMv7 classic ARMs.

gfx.cpp

@@ -191,7 +191,7 @@ void S9xStartScreenRefresh (void)
 		memset(GFX.SubZBuffer, 0, GFX.ScreenSize);
 	}
 
-	if (++IPPU.FrameCount % Memory.ROMFramesPerSecond == 0)
+	if (++IPPU.FrameCount == (uint32)Memory.ROMFramesPerSecond)
 	{
 		IPPU.DisplayedRenderedFrameCount = IPPU.RenderedFramesCount;
 		IPPU.RenderedFramesCount = 0;