do not use 'colon' sign in the iSerialNumber field of USB descriptor (#7225)

Author: lyusupov

Diff for: cores/esp32/USB.cpp

@@ -165,7 +165,7 @@ bool ESPUSB::begin(){
             StreamString s;
             uint8_t m[6];
             esp_efuse_mac_get_default(m);
-            s.printf("%02X:%02X:%02X:%02X:%02X:%02X", m[0], m[1], m[2], m[3], m[4], m[5]);
+            s.printf("%02X%02X%02X%02X%02X%02X", m[0], m[1], m[2], m[3], m[4], m[5]);
             serial_number = s;
         }
 #endif