nvme-pci: add missing unlock for reset error

The reset work holds a mutex to prevent races with removal modifying the
same resources, but was unlocking only on success. Unlock on failure
too.

Fixes: 5c959d73 ("nvme-pci: fix rapid add remove sequence")
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>