libxfs: fix up mismerge in libxfs_iflush_int

libxfs: fix up mismerge in libxfs_iflush_int

XFS_ISDIR is a bool, don't compare it to S_IFDIR

e37bf5 xfs: mode di_mode to vfs inode had a small mis-merge
from kernelspace, when moving from

	if ((ip->i_d.di_mode & S_IFMT) == S_IFDIR)
to
	if (XFS_ISDIR(ip) == S_IFDIR

that "==" should have been dropped.

Signed-off-by: ERic Sandeen <sandeen@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>