Apply same idiom as in 5000 introduced by
'iwlwifi: define firmware file name once'
Signed-off-by: NTomas Winkler <tomas.winkler@intel.com>
Signed-off-by: NReinette Chatre <reinette.chatre@intel.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>