netxen: fix memory leak in drivers/net/netxen_nic_init.c

For kernel bugzilla #12537:
http://bugzilla.kernel.org/show_bug.cgi?id=12537

Free memory.

Signed-off-by: Daniel Marjamäki <danielm77@spray.se>
Signed-off-by: David S. Miller <davem@davemloft.net>