iwlwifi: clear STATUS_SCAN_HW when PAN_PARAMS fails

The STATUS_SCAN_HW is set before calling iwlagn_set_pan_params
(used as an input to calculate slot time allocation). The bit needs
to be cleared in case sending the command fails.

Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Ilan Peer <ilan.peer@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>