cfg80211: Fix use after free when process wdev events

"bssid" is only initialized out of the while loop, in case of two
events with same type: EVENT_CONNECT_RESULT, but one has zero
ether addr, the other is non-zero, the bssid pointer will be
referenced twice, which lead to use-after-free issue.

Change-Id: Ie8a24275f7ec5c2f936ef0a802a42e5f63be9c71
CRs-Fixed: 2254305
Signed-off-by: Zhu Jianmin <jianminz@codeaurora.org>