hw tune (#1519)

* Update appmain.c

Patch to fix incorrect lf voltage reading when no lf antenna is connected.
v_lf134, v_lf125 should be set to 0 in case they are not updated later and leave it with an invalid random value.

armsrc/appmain.c

@@ -163,7 +163,9 @@ static void MeasureAntennaTuning(void) {
         uint8_t results[256];
     } PACKED payload;
 
-    memset(payload.results, 0, sizeof(payload.results));
+    // Need to clear all values to ensure non-random responses.
+    memset(&payload, 0, sizeof(payload));
+    // memset(payload.results, 0, sizeof(payload.results));
 
     sample_config *sc = getSamplingConfig();
     payload.divisor = sc->divisor;