Fix channel validity check

Fixed mistaken channel validity check in `tilt_stop` funciton
in multi mode. Refs #1111 and fixes #1114.

src/relay_chn_tilt.c

@@ -291,7 +291,7 @@ void relay_chn_tilt_reverse_all()
 
 void relay_chn_tilt_stop(uint8_t chn_id)
 {
-    if (!relay_chn_is_channel_id_valid(chn_id)) {
+    if (relay_chn_is_channel_id_valid(chn_id)) {
         relay_chn_tilt_dispatch_cmd(&s_tilt_ctls[chn_id], RELAY_CHN_TILT_CMD_STOP);
     }
 }