xfs: Sanity check flags of Q_XQUOTARM call

commit 3dd4d40b upstream.

Flags passed to Q_XQUOTARM were not sanity checked for invalid values.
Fix that.

Fixes: 9da93f9b ("xfs: fix Q_XQUOTARM ioctl")
Reported-by: Yang Xu <xuyang2018.jy@cn.fujitsu.com>
Signed-off-by: Jan Kara <jack@suse.cz>
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>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>