Reverting a change introduced in 6de7e7f8b3698 "[drm] upstream sync to v4.10"
(upstream c470abd4fde40ea).

Index: src/drivers/gpu/drm/mgag200/mgag200_mode.c
===================================================================
--- src.orig/drivers/gpu/drm/mgag200/mgag200_mode.c	2017-06-20 20:40:11.261262778 +0200
+++ src/drivers/gpu/drm/mgag200/mgag200_mode.c	2017-06-20 20:40:39.610842564 +0200
@@ -1394,20 +1394,19 @@
  * use this for 8-bit mode so can't perform smooth fades on deeper modes,
  * but it's a requirement that we provide the function
  */
-static int mga_crtc_gamma_set(struct drm_crtc *crtc, u16 *red, u16 *green,
-			      u16 *blue, uint32_t size)
+static void mga_crtc_gamma_set(struct drm_crtc *crtc, u16 *red, u16 *green,
+			       u16 *blue, uint32_t start, uint32_t size)
 {
 	struct mga_crtc *mga_crtc = to_mga_crtc(crtc);
+	int end = (start + size > MGAG200_LUT_SIZE) ? MGAG200_LUT_SIZE : start + size;
 	int i;
 
-	for (i = 0; i < size; i++) {
+	for (i = start; i < end; i++) {
 		mga_crtc->lut_r[i] = red[i] >> 8;
 		mga_crtc->lut_g[i] = green[i] >> 8;
 		mga_crtc->lut_b[i] = blue[i] >> 8;
 	}
 	mga_crtc_load_lut(crtc);
-
-	return 0;
 }
 
 /* Simple cleanup function */