libxfs: don't propagate RTINHERIT -> REALTIME when there is no rtdev

libxfs: don't propagate RTINHERIT -> REALTIME when there is no rtdev

When creating a file inside a directory that has RTINHERIT set, only
propagate the REALTIME flag to the file if the filesystem actually has a
realtime volume configured.  Otherwise, we end up writing inodes that
trip the verifiers.

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