scan: if ellsi_check fails, return the lastState (and don't call ourselves recursively)

MultiCAN/src/drivers/scan/ellsi.c

@@ -316,9 +316,9 @@ static int ellsi_check(int sock) {
             ntohl(ack.payload.lastSubcommand),
             ntohl(ack.payload.lastState));
     } else {
-        return ellsi_check(sock);
+        return -1;
     }
-    return 0;
+    return ack.payload.lastState;
 }
 
 static int ellsi_register(ellsi_state_t *state) {