Returning pool id (i.e. >= 0) from a sysfs ->store() callback makes
userspace think it needs to retry the write.  Fix it - it's a leftover
from the times when the equivalent of rbd_dev_create() was the first
action in rbd_add().
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
        struct rbd_spec *spec = NULL;
        struct rbd_client *rbdc;
        bool read_only;
-       int rc = -ENOMEM;
+       int rc;
 
        if (!try_module_get(THIS_MODULE))
                return -ENODEV;
        }
 
        rbd_dev = rbd_dev_create(rbdc, spec, rbd_opts);
-       if (!rbd_dev)
+       if (!rbd_dev) {
+               rc = -ENOMEM;
                goto err_out_client;
+       }
        rbdc = NULL;            /* rbd_dev now owns this */
        spec = NULL;            /* rbd_dev now owns this */
        rbd_opts = NULL;        /* rbd_dev now owns this */