xfs: fix inobt magic number check

xfs: fix inobt magic number check

Source kernel commit: 2e050e648ad6c74a2f0a28f645155128be0626ca

In commit a6a781a58befcbd467c ("xfs: have buffer verifier functions
report failing address") the bad magic number return was ported
incorrectly.

Fixes: a6a781a58befcbd467ce843af4eaca3906aa1f08
Reported-by: syzbot+08ab33be0178b76851c8@syzkaller.appspotmail.com
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>