P2P: Do not accept any BSS entry for join if SSID is already known

P2P: Do not accept any BSS entry for join if SSID is already known

Use wpa_bss_get() with the specific Group SSID instead of
wpa_bss_get_bssid_latest() if the SSID is already known. This makes the
P2P join operations more robust in case the frequency of the group was
not yet known and the same P2P Interface Address may have been used in
multiple group instances with an older group entry still present in the
cached scan results.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>