bna: add missing iounmap() on error in bnad_init()

Add the missing iounmap() before return from bnad_init()
in the error handling case.
Introduced by commit 01b54b1451853593739816a392485c4e2bee7dda
(bna: tx rx cleanup fix).

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>