drm/nouveau: off by one in nouveau_drm_vblank_enable()

The test here should be ">= ARRAY_SIZE()" instead of "> ARRAY_SIZE()".

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>