nvme: update firmware version after commit

The firmware version sysfs entry needs to be updated after a successfully
firmware activation.

nvme-cli stopped issuing an Identify Controller command to list the
current firmware information and relies on sysfs showing the current
firmware version.

Reported-by: Kenji Tomonaga <tkenbo@gmail.com>
Signed-off-by: Daniel Wagner <dwagner@suse.de>
Tested-by: Kenji Tomonaga <tkenbo@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Niklas Cassel <niklas.cassel@wdc.com>
[fixed off-by one afi index]
Signed-off-by: Keith Busch <kbusch@kernel.org>