nvme: Fix number of blocks detection

NVMe should use the nsze value from the queried device. This will
reflect the total number of blocks of the device and fix detecting
my Samsung 960 EVO 256GB.

Original:
Capacity: 40386.6 MB = 39.4 GB (82711872 x 512)

Fixed:
Capacity: 238475.1 MB = 232.8 GB (488397168 x 512)

Signed-off-by: Jon Nettleton <jon@solid-run.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Tom Rini <trini@konsulko.com>