iwlwifi: mvm: handle device start failures during restart

If the device fails during a restart, mac80211 now handles the
situation better but we still have a little bit of cleanup to
do in the driver - add the required code.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Reviewed-by: ArikX Nemtsov <arik@wizery.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>