libertas: fix sanity check on sequence number in command response

Slightly more useful if we compare it against the sequence number of the
command we have outstanding, rather than comparing the reply with itself.

Doh. Pointed out by Sebastian Siewior

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Acked-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>