nvme: use proper mask to get correct lbafu value

nvme: use proper mask to get correct lbafu value

The NVME_NS_FLBAS_HIGHER/LOWER_MASK is used to get the format index
value from Formatted LBA Size (FLBAS) field of Identify Namespace
Data Structure. But, We are not getting the proper lbafu value while
using the same macro on user passed format index value.
So, use the proper mask to get the correct lbafu value.

Signed-off-by: Francis Pravin <francis.p@samsung.com>
Reviewed-by: Steven Seungcheol Lee <sc108.lee@samsung.com>