create-ns: align the namespaces to 1Mib boundaries when using SI suffixes

create-ns: align the namespaces to 1Mib boundaries when using SI suffixes

Some controllers refuse to create namespaces with a size not aligned to
a 1 MiB boundary, this happens when using the -S and -C options.

$ nvme create-ns /dev/nvme0 -S 80M -C 80M -f 0
NVMe status: Invalid Field in Command: A reserved coded value or
an unsupported value in a defined field(0x2)

Fix this problem by modifying create_ns() parse_lba_num_si() to align
the values to 1 MiB boundaries. If granularity is supported, we will
use the specified values, if they are smaller than 1 MiB.

Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>