drm/nouveau: unwind on load errors

nouveau_load() just returned directly if there was an error instead of
releasing resources.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Reviewed-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Signed-off-by: Francisco Jerez <currojerez@riseup.net>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>