mkfs: disallow specifying the sector size of internal log

mkfs: disallow specifying the sector size of internal log

If the log is on the data device (i.e. internal) then it should
match the sector size the data device is using. If they don't match,
then one or the other doesn't have atomic sector writes and we could
have crash consistency problems. Not to mention that it's simply
wrong to have two different sector sizes for the same device.

Hence enforce the requirement that an internal log device always has
the same sector size as the data device.

Signed-Off-By: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>