drm/i915: Bad pixel formats can't reach the sprite code

The framebuffer pixel format is already checked by the common code.
So there's no way an invalid format could reach the driver. So instead
of falling back to a default format, call BUG().
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NJesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_sprite.c

@@ -79,9 +79,7 @@ ivb_update_plane(struct drm_plane *plane, struct drm_framebuffer *fb,
 		sprctl |= SPRITE_FORMAT_YUV422 | SPRITE_YUV_ORDER_VYUY;
 		break;
 	default:
-		DRM_DEBUG_DRIVER("bad pixel format, assuming RGBX888\n");
-		sprctl |= SPRITE_FORMAT_RGBX888;
-		break;
+		BUG();
 	}
 
 	if (obj->tiling_mode != I915_TILING_NONE)
@@ -263,9 +261,7 @@ ilk_update_plane(struct drm_plane *plane, struct drm_framebuffer *fb,
 		dvscntr |= DVS_FORMAT_YUV422 | DVS_YUV_ORDER_VYUY;
 		break;
 	default:
-		DRM_DEBUG_DRIVER("bad pixel format, assuming RGBX888\n");
-		dvscntr |= DVS_FORMAT_RGBX888;
-		break;
+		BUG();
 	}
 
 	if (obj->tiling_mode != I915_TILING_NONE)