iwlwifi/iwl-drv.c: fix typo defualt -> default

trivial, but this is user visible b/c it is in the help text

Signed-off-by: Toralf Förster <toralf.foerster@gmx.de>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>