drm/nouveau/bar/nv50: check bar1 vmm return value

commit 307a312df9c43fdea286ad17f748aaf777cc434a upstream.

Check bar1's new vmm creation return value for errors.

Signed-off-by: Jon Derrick <jonathan.derrick@intel.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Sushma Kalakota <sushmax.kalakota@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>