netxen: fix firmware download warnings

Fix following warnings, by using integer firmware types.

drivers/net/netxen/netxen_nic_hw.c: In function 'netxen_load_firmware':
drivers/net/netxen/netxen_nic_hw.c:1146: warning: comparison with string literal results in unspecified behavior
drivers/net/netxen/netxen_nic_hw.c:1146: warning: comparison with string literal results in unspecified behavior
drivers/net/netxen/netxen_nic_hw.c:1146: warning: comparison with string literal results in unspecified behavior
drivers/net/netxen/netxen_nic_hw.c:1159: warning: comparison with string literal results in unspecified behavior
drivers/net/netxen/netxen_nic_hw.c:1159: warning: comparison with string literal results in unspecified behavior
drivers/net/netxen/netxen_nic_hw.c:1159: warning: comparison with string literal results in unspecified behavior

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Dhananjay Phadke <dhananjay@netxen.com>
Signed-off-by: David S. Miller <davem@davemloft.net>