be2net: add unlock on error path

The unlock accidentally got removed from the error path in dd131e76:
"be2net: Bug fix to avoid disabling bottom half during firmware upgrade."

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Sarveshwar Bandi <sarveshwarb@serverengines.com>
Signed-off-by: David S. Miller <davem@davemloft.net>