drm/rockchip: vop: call vop_cfg_done() under reg_lock

The function vop_cfg_done() is a simple VOP_REG_SET(). As such it should
be done under a reg_lock. A quick look through the driver shows that all
other instances (apart from driver init) have the lock. Do the same here

Cc: Sandy Huang <hjc@rock-chips.com>
Cc: Heiko Stübner <heiko@sntech.de>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Sandy Huang <hjc@rock-chips.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200505151613.2932456-1-emil.l.velikov@gmail.com

drivers/gpu/drm/rockchip/rockchip_drm_vop.c

@@ -645,10 +645,10 @@ static int vop_enable(struct drm_crtc *crtc, struct drm_crtc_state *old_state)
 		s->enable_afbc = false;
 	}
 
-	spin_unlock(&vop->reg_lock);
-
 	vop_cfg_done(vop);
 
+	spin_unlock(&vop->reg_lock);
+
 	/*
 	 * At here, vop clock & iommu is enable, R/W vop regs would be safe.
 	 */