nvme: use helper nvme_ctrl_state in nvme_keep_alive_finish function

[ Upstream commit 599d9f3a ]

We no more need acquiring ctrl->lock before accessing the
NVMe controller state and instead we can now use the helper
nvme_ctrl_state. So replace the use of ctrl->lock from
nvme_keep_alive_finish function with nvme_ctrl_state call.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Stable-dep-of: 84488282 ("Revert "nvme: make keep-alive synchronous operation"")
Signed-off-by: Sasha Levin <sashal@kernel.org>