xfs: fix uninitialized variable access

If the end position of a GETFSMAP query overlaps an allocated space and
we're using the free space info to generate fsmap info, the akeys
information gets fed into the fsmap formatter with bad results.
Zero-init the space.

Reported-by:  <syzbot+090ae72d552e6bd93cfe@syzkaller.appspotmail.com>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>

fs/xfs/xfs_fsmap.c

@@ -761,6 +761,7 @@ xfs_getfsmap_datadev_bnobt(
 {
 	struct xfs_alloc_rec_incore	akeys[2];
 
+	memset(akeys, 0, sizeof(akeys));
 	info->missing_owner = XFS_FMR_OWN_UNKNOWN;
 	return __xfs_getfsmap_datadev(tp, keys, info,
 			xfs_getfsmap_datadev_bnobt_query, &akeys[0]);