[SCSI] qla2xxx: Reset seconds_since_last_heartbeat correctly.

The seconds_since_last_heartbeat should be checked for consecutive
heartbeat checks. Currently it could happen that seconds_since_last_heartbeat
gets set to max (2 seconds) for non-consecutive heartbeat checks.

Signed-off-by: Giridhar Malavali <giridhar.malavali@qlogic.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>