drm/rockchip: vop: Fix call to crtc reset helper

Allocation of crtc_state may fail in vop_crtc_reset, causing an invalid
pointer to be passed to __drm_atomic_helper_crtc_reset.

Fix this by adding a NULL check of crtc_state, similar to other drivers.

Fixes: 01e2eaf4

 ("drm/rockchip: Convert to using __drm_atomic_helper_crtc_reset() for reset.")
Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230621223311.2239547-4-jonas@kwiboo.se