nvme-rdma: initialize ret to zero to avoid returning garbage

ret is not initialized so it contains garbage.  Ensure garbage
is not returned by initializing rc to 0.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>

drivers/nvme/host/rdma.c

@@ -1319,7 +1319,7 @@ out_destroy_queue_ib:
 static int nvme_rdma_device_unplug(struct nvme_rdma_queue *queue)
 {
 	struct nvme_rdma_ctrl *ctrl = queue->ctrl;
-	int ret;
+	int ret = 0;
 
 	/* Own the controller deletion */
 	if (!nvme_change_ctrl_state(&ctrl->ctrl, NVME_CTRL_DELETING))