mwifiex: Report connected BSS with cfg80211_connect_bss()

When a network is moved or reconfigured on the different channel, there
can be multiple BSSes with the same BSSID and SSID in scan result
before the old one expires. Then, it can cause cfg80211_connect_result
to map current_bss to a bss with the wrong channel.

Let mwifiex_cfg80211_assoc return the selected BSS and then the caller
can report it cfg80211_connect_bss.

Signed-off-by: Yen-lin Lai <yenlinlai@chromium.org>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210201070649.1667209-1-yenlinlai@chromium.org