ath10k: fix the invalid STA disconnect after wow resume

Clear the previous wakeup reason data and reset the wakeup
reason event field to avoid the STA disconnect with invalid
wow event.

CRs-Fixed: 2199100
Change-Id: If45b5ae6e6f93ab9068b59a5e31f46b829363936
Signed-off-by: Sarada Prasanna Garnayak <sgarna@codeaurora.org>