drm/nouveau/kms/nv50: add null check before pointer dereference

Add null check before dereferencing pointer asyc

Addresses-Coverity-ID: 1397932
Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
1 file changed