SAE: Use BSSID stored in ext_auth_bssid for set_pmk

SAE: Use BSSID stored in ext_auth_bssid for set_pmk

pending_bssid is cleared in the connected state and thus is not valid if
SAE authentication is done to a new BSSID when in the connected state.
Hence use the BSSID from ext_auth_bssid while configuring the PMK for
the external authentication case. This is required for roaming to a new
BSSID with driver-based-SME while the SAE processing happens with
wpa_supplicant.

Signed-off-by: Jouni Malinen <jouni@codeaurora.org>