iwlwifi: avoid code duplication in stopping fw debug data recording

Make all FW debug data stop recording flows to use
iwl_fw_dbg_stop_recording function instead of writing to FW
registers directly.

Signed-off-by: Shahar S Matityahu <shahar.s.matityahu@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>