rockchip: video: rk_vop: add grf field

The last set of rebases had dropped the 'grf' field from the common
rk_vop.  Add this back to un-break the build (and driver).

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>

drivers/video/rockchip/rk_vop.h

@@ -10,6 +10,7 @@
 #include <asm/arch/vop_rk3288.h>
 
 struct rk_vop_priv {
+	void *grf;
 	void *regs;
 };