drm/nouveau: fix failure path if userspace specifies no valid memtypes

We need to add the buffer to the list even if we fail, otherwise the
validate_fini() call won't unreserve + unreference the GEM object,
making TTM very unhappy.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_gem.c

@@ -321,6 +321,7 @@ retry:
 		else {
 			NV_ERROR(dev, "invalid valid domains: 0x%08x\n",
 				 b->valid_domains);
+			list_add_tail(&nvbo->entry, &op->both_list);
 			validate_fini(op, NULL);
 			return -EINVAL;
 		}