iwlwifi: remove duplicate initialization in __iwl_down()

We initialize exit_pending twice.  It's the second initialization which
is correct.  That was added in d745d472

 "iwlwifi: cancel scan when
down the device".

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>