Fix: memset results first time

Refs: #4

src/main/esp32_eurorack_generic.c

@@ -1,4 +1,5 @@
 #include <stdio.h>
+#include <string.h>
 
 #include "esp_attr.h"
 #include "esp_err.h"
@@ -114,6 +115,8 @@ void app_main(void)
   esp_err_t adc_ret;
   uint32_t ret_num = 0;
   uint8_t result[ADC_READ_LEN] = {0};
+  /* Fill result with 0xcc */
+  memset(result, 0xcc, ADC_READ_LEN);
 
   while (1) {
     /* Perform a read */