_scratch_mkfs_geom: Fix regex used for matching block size option

_scratch_mkfs_geom: Fix regex used for matching block size option

The regular expression used by _scratch_mkfs_geom() to match mkfs.xfs' block
size argument interprets the character 'b' as optional. It should actually
interpret whitespace as optional.

This causes generic/223 to fail when testing an XFS filesystem which uses an
external log device along with the -lsize option. In this case, the original
value of -lsize is replaced with the value of $blocksize.

_scratch_mkfs_sized() also uses the same incorrect regex.

Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Zorro Lang <zlang@kernel.org>