wifi: iwlwifi: restore missing initialization of async_handlers_list (again)

The initialization of async_handlers_list
was accidentally removed in a previous change.

Then it was restoted by commit 175e69e3 ("wifi: iwlwifi: restore
missing initialization of async_handlers_list").

Somehow, the initialization disappeared again.
Restote it.

Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>