P2P: Fix removal_reason setting to use correct pointer

The previous version triggered a NULL pointer dereference on
P2P_GROUP_REMOVE * command.

wpa_supplicant/p2p_supplicant.c

@@ -2807,7 +2807,7 @@ int wpas_p2p_group_remove(struct wpa_supplicant *wpa_s, const char *ifname)
 		while (wpa_s) {
 			prev = wpa_s;
 			wpa_s = wpa_s->next;
-			wpa_s->removal_reason = P2P_GROUP_REMOVAL_REQUESTED;
+			prev->removal_reason = P2P_GROUP_REMOVAL_REQUESTED;
 			wpas_p2p_group_delete(prev);
 		}
 		return 0;