LWIS: Fix the deadlock between event clear and emit.

Change lwis_client_event_states_clear() to collect all the event states
first and then clear them afterwards.

Bug: 175221839
Test: manually test the board boots, open and close AOSP camera app
works fine.

Change-Id: Ie12d186f7c14154a24a67441df70ea51cdb914ca
Signed-off-by: Ge Bian <bian@google.com>