Don't recalculate length in every iteration

Author: askask

wled00/e131.cpp

@@ -97,9 +97,10 @@ void handleE131Packet(e131_packet_t* p, IPAddress clientIP, byte protocol){
   uint8_t artnetOffset = (protocol == P_ARTNET) ? -1 : 0;
 
   #ifdef WLED_ENABLE_DMX
+  uint16_t dmxLength = dmxChannels + artnetOffset;
   // does not act on out-of-order packets yet
   if (e131ProxyUniverse > 0 && uni == e131ProxyUniverse) {
-    for (uint16_t i = 1+artnetOffset; i <= dmxChannels+artnetOffset; i++)
+    for (uint16_t i = 1+artnetOffset; i <= dmxLength; i++)
       dmx.write(i, e131_data[i]);
     dmx.update();
   }