nvme-pci: properly report state change failure in nvme_reset_work

If the state change to NVME_CTRL_CONNECTING fails, the dmesg is going to
be like:

  [  293.689160] nvme nvme0: failed to mark controller CONNECTING
  [  293.689160] nvme nvme0: Removing after probe failure status: 0

Even it prints the first line to indicate the situation, the second line
is not proper because the status is 0 which means normally success of
the previous operation.

This patch makes it indicate the proper error value when it fails.
  [   25.932367] nvme nvme0: failed to mark controller CONNECTING
  [   25.932369] nvme nvme0: Removing after probe failure status: -16

This situation is able to be easily reproduced by:
  root@target:~# rmmod nvme && modprobe nvme && rmmod nvme
Signed-off-by: Minwoo Im <minwoo.im.dev@gmail.com>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/pci.c

@@ -2517,6 +2517,7 @@ static void nvme_reset_work(struct work_struct *work)
 	if (!nvme_change_ctrl_state(&dev->ctrl, NVME_CTRL_CONNECTING)) {
 		dev_warn(dev->ctrl.device,
 			"failed to mark controller CONNECTING\n");
+		result = -EBUSY;
 		goto out;
 	}