drm/mediatek: plane: Use FB's format's cpp to compute x offset

Use the framebuffer's format to compute its cpp, and use it when
calculating the address shift value.
Signed-off-by: NBibby Hsieh <bibby.hsieh@mediatek.com>
Signed-off-by: NSean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1470279597-60453-7-git-send-email-bibby.hsieh@mediatek.com

drivers/gpu/drm/mediatek/mtk_drm_plane.c

@@ -135,7 +135,7 @@ static void mtk_plane_atomic_update(struct drm_plane *plane,
 	pitch = fb->pitches[0];
 	format = fb->pixel_format;
 
-	addr += (plane->state->src.x1 >> 16) * 4;
+	addr += (plane->state->src.x1 >> 16) * drm_format_plane_cpp(format, 0);
 	addr += (plane->state->src.y1 >> 16) * pitch;
 
 	state->pending.enable = true;