hw/block/nvme: report actual LBA data shift in LBAF

hw/block/nvme: report actual LBA data shift in LBAF

Calculate the data shift value to report based on the set value of
logical_block_size device property.

In the process, use a local variable to calculate the LBA format
index instead of the hardcoded value 0. This makes the code more
readable and it will make it easier to add support for multiple LBA
formats in the future.

Signed-off-by: Dmitry Fomichev <dmitry.fomichev@wdc.com>
Reviewed-by: Klaus Jensen <k.jensen@samsung.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>