Fix WNM-Sleep Mode exit debug print of BIGTK

Previous debug print used IGTK instead of BIGTK, so fix that to use the
correct key. Actual generation of the BIGTK subelement itself was using
the correct key, though, so this is only needed to fix the debug print.

Signed-off-by: Jouni Malinen <j@w1.fi>

src/ap/wpa_auth.c

@@ -4267,7 +4267,7 @@ int wpa_wnmsleep_bigtk_subelem(struct wpa_state_machine *sm, u8 *pos)
 	wpa_printf(MSG_DEBUG, "WNM: BIGTK Key ID %u in WNM-Sleep Mode exit",
 		   gsm->GN_bigtk);
 	wpa_hexdump_key(MSG_DEBUG, "WNM: BIGTK in WNM-Sleep Mode exit",
-			gsm->IGTK[gsm->GN_bigtk - 6], len);
+			gsm->BIGTK[gsm->GN_bigtk - 6], len);
 
 	return pos - start;
 }