drm: verisilicon: call atomic helper's plane state check even if no CRTC

drm: verisilicon: call atomic helper's plane state check even if no CRTC

The `drm_atomic_helper_check_plane_state()` helper function needs to be
called even if the plane is bound to no CRTCs.

Remove the early return in the primary plane's atomic_check, and use
NULL for crtc_state in this situation.

Fixes: dbf21777caa8 ("drm: verisilicon: add a driver for Verisilicon display controllers")
Signed-off-by: Icenowy Zheng <zhengxingda@iscas.ac.cn>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patch.msgid.link/20260331060126.1291966-4-zhengxingda@iscas.ac.cn