xfs: = vs == typo in ASSERT()

There is a '=' vs '==' typo so the ASSERT()s are always true.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Ben Myers <bpm@sgi.com>