xfs: disable per-inode DAX flag

commit 742d84290739ae908f1b61b7d17ea382c8c0073a upstream.

Currently flag switching can be used to easily crash the kernel.  Disable
the per-inode DAX flag until that is sorted out.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>