bna: unlock on error path in pnad_pci_probe()

We introduced a new lock here, so there was error path which needs
an unlock now.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Rasesh Mody <rmody@brocade.com>
Signed-off-by: David S. Miller <davem@davemloft.net>