[CONNECTOR]: Fix warning in cn_queue.c

cn_queue.c:130: warning: value computed is not used

There is no point in testing the atomic value if the result is thrown
away.

From Evgeniy:

It was created to put implicit smp barrier, but it is not needed there.

Signed-off-by: Andreas Schwab <schwab@suse.de>
Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>