brcmfmac: clear eventmask array before using it

When the event_msgs iovar is set an array is used to configure the
enabled events. This arrays needs to nulled before configuring
otherwise unhandled events will be enabled. This solves a problem
where in case of wowl the host got woken by an incorrectly enabled
event.

Reviewed-by: Pieter-Paul Giesberts <pieter-paul.giesberts@broadcom.com>
Reviewed-by: Arend Van Spriel <arend@broadcom.com>
Signed-off-by: Hante Meuleman <hante.meuleman@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>