man: update mkfs.xfs inode flag option documentation

man: update mkfs.xfs inode flag option documentation

The mkfs manpage says that the extent size, cow extent size, realtime,
and project id inheritance bits are passed on to "newly created
children".  This isn't technically true -- it's only passed on to newly
created regular files and directories.  It is not passed on to special
files.

Fix this minor inaccuracy in the documentation.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>