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

While running generic/042 with -drtinherit=1 set in MKFS_OPTIONS, I
observed that the kernel will gladly set the realtime flag on any file
created on the loopback filesystem even though that filesystem doesn't
actually have a realtime device attached.  This leads to verifier
failures and doesn't make any sense, so be smarter about this.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/xfs_inode.c

@@ -717,7 +717,8 @@ xfs_inode_inherit_flags(
 		if (pip->i_d.di_flags & XFS_DIFLAG_PROJINHERIT)
 			di_flags |= XFS_DIFLAG_PROJINHERIT;
 	} else if (S_ISREG(mode)) {
-		if (pip->i_d.di_flags & XFS_DIFLAG_RTINHERIT)
+		if ((pip->i_d.di_flags & XFS_DIFLAG_RTINHERIT) &&
+		    xfs_sb_version_hasrealtime(&ip->i_mount->m_sb))
 			di_flags |= XFS_DIFLAG_REALTIME;
 		if (pip->i_d.di_flags & XFS_DIFLAG_EXTSZINHERIT) {
 			di_flags |= XFS_DIFLAG_EXTSIZE;