bna: Semaphore Lock Fix

Remove a BUG_ON() as it is not required.

Change the unconditional write to release a semaphore to read sem first
and then write. This will eliminate the possibility of sem getting locked
while trying to release it in case if previous sem_get operation failed.

Signed-off-by: Gurunatha Karaje <gkaraje@brocade.com>
Signed-off-by: Rasesh Mody <rmody@brocade.com>
Signed-off-by: David S. Miller <davem@davemloft.net>