ath11k: fix ZERO address in probe request

Host needs to pass at least on bssid with all 0xff to firmware in
WMI_START_SCAN_CMDID, otherwise the bssid and receiver address
in probe requeste are all ZEROs.

This also fixed some hidden AP connection issue because some AP
doesn't respond to probe request which receiver address are all
ZEROs.

Tested-on: QCA6390 hw2.0 PCI WLAN.HST.1.0.1-01740-QCAHSTSWPLZ_V2_TO_X86-1

Signed-off-by: Carl Huang <cjhuang@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201012101733.24137-1-cjhuang@codeaurora.org