NET: bna, fix lock imbalance

bnad_set_rx_mode omit to unlock bna_lock on one fail path. Fix that.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Debashis Dutt <ddutt@brocade.com>
Cc: Rasesh Mody <rmody@brocade.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: David S. Miller <davem@davemloft.net>