xfs: compat_ioctl: use compat_ptr()

For 31-bit s390 user space, we have to pass pointer arguments through
compat_ptr() in the compat_ioctl handler.

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