netxen: fix firmware type check

Unified firmware image may not contain MN type of firmware.
Driver should fall back to NOMN firmware type instead
of going to flash.

Signed-off-by: Dhananjay Phadke <dhananjay@netxen.com>
Signed-off-by: Amit Kumar Salecha <amit.salecha@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>