xfs: fix scrub flagging rtinherit even if there is no rt device

[ Upstream commit c1f6b1ac ]

The kernel has always allowed directories to have the rtinherit flag
set, even if there is no rt device, so this check is wrong.

Fixes: 80e4e126 ("xfs: scrub inodes")
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>