iwlwifi: remove redundant initialization of final_mode

Problem identified by Miguel Botón <mboton.lkml@gmail.com>, alternate
solution suggested by Zhu Yi <yi.zhu@intel.com>, patch by me. :-)

Cc: Miguel Botón <mboton.lkml@gmail.com>
Cc: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>