generic/223: Don't clear MKFS_OPTION before calling _scratch_mkfs_geom()

generic/223: Don't clear MKFS_OPTION before calling _scratch_mkfs_geom()

Current _scratch_mkfs_geom() adds geometry parameters to the end of the
MKFS_OPTIONS blindly.  ext4 can accept the last one if geometry parameters
and original MKFS_OPTION have the same mkfs options but xfs cannot accept
them and reports "xxx option is respecified" error.  Make _scratch_mkfs_geom()
override the same mkfs options in original MKFS_OPTION by geometry parameters.

With this change, generic/223 doesn't need to clear original MKFS_OPTION
before calling _scratch_mkfs_geom() and can use other mkfs options in original
MKFS_OPTION.

Signed-off-by: Xiao Yang <yangx.jy@cn.fujitsu.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>