drm/kms: fix fb_changed = true else statement

a patch from Roel was wrong, fix this properly, really
if the fb ptrs are different fb changed shuold be true.
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_crtc_helper.c

@@ -836,11 +836,7 @@ int drm_crtc_helper_set_config(struct drm_mode_set *set)
 			mode_changed = true;
 		} else if (set->fb == NULL) {
 			mode_changed = true;
-		} else if ((set->fb->bits_per_pixel !=
-			 set->crtc->fb->bits_per_pixel) ||
-			 set->fb->depth != set->crtc->fb->depth)
-			fb_changed = true;
-		else
+		} else
 			fb_changed = true;
 	}