drm/rockchip: vop2: Use regcache_sync() to fix suspend/resume

afa965a4 ("drm/rockchip: vop2: fix suspend/resume") uses
regmap_reinit_cache() to fix the suspend/resume issue with the VOP2
driver. During discussion it came up that we should rather use
regcache_sync() instead. As the original patch is already applied
fix this up in this follow-up patch.

Fixes: afa965a4

 ("drm/rockchip: vop2: fix suspend/resume")
Cc: stable@vger.kernel.org
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230417123747.2179695-1-s.hauer@pengutronix.de