iwlwifi: dbg: remove iwl_fw_cancel_dumps function

Use cancel_delayed_work_sync on the dump workers only in case of
unloading the op mode. In any other case use iwl_fw_flush_dumps or
iwl_fw_dbg_stop_sync (depends if the op mode mutex is held or not).
This way, the driver will wait until debug data is collected in all
cases but op mode unloading.

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