nvmet: Fix nvmet_execute_write_zeroes sector count

We have to increment the number of logical blocks to a 1's based value
in the native format prior to converting to 512b units.

Signed-off-by: Rodrigo R. Galvao <rosattig@linux.vnet.ibm.com>
[changelog]
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>