iwl4965: fix return code indicating one interface is supported

This is a fix to patch "iwlwifi: fix iwl_mac_add_interface handler".
In that patch the return code was corrected for iwl3945, but not for
iwl4965.

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Cc: Tomas Carnecky <tom@dbservice.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>