rbd: refactor rbd_init() a bit

Refactor rbd_init() a bit to make it more clear what's going on.
Signed-off-by: NIlya Dryomov <ilya.dryomov@inktank.com>
Reviewed-by: NAlex Elder <elder@linaro.org>
Reviewed-by: NJosh Durgin <josh.durgin@inktank.com>

drivers/block/rbd.c

@@ -5292,18 +5292,22 @@ static int __init rbd_init(void)
 
 	if (!libceph_compatible(NULL)) {
 		rbd_warn(NULL, "libceph incompatibility (quitting)");
-
 		return -EINVAL;
 	}
+
 	rc = rbd_slab_init();
 	if (rc)
 		return rc;
+
 	rc = rbd_sysfs_init();
 	if (rc)
-		rbd_slab_exit();
-	else
-		pr_info("loaded\n");
+		goto err_out_slab;
 
+	pr_info("loaded\n");
+	return 0;
+
+err_out_slab:
+	rbd_slab_exit();
 	return rc;
 }