drm/nouveau/kms/nv50-: Use NV_ATOMIC() in nv50_head_atomic_check_lut()

Since this is used in the atomic check, we should use the right debug macro
for it.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Martin Peres <martin.peres@free.fr>
Cc: Jeremy Cline <jcline@redhat.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Link: https://gitlab.freedesktop.org/drm/nouveau/-/merge_requests/10