HardwareSerial: fix begin() lock issue on error path (#8182)

* HardwareSerial: fix begin() lock issue on error path

If the user supplied a wrong UART number, the begin() method would
return without releasing the lock. Add missing unlock call.

* removing unsed Case test

---------
Co-authored-by: Rodrigo Garcia <rodrigo.garcia@espressif.com>

cores/esp32/HardwareSerial.cpp

@@ -365,9 +365,6 @@ void HardwareSerial::begin(unsigned long baud, uint32_t config, int8_t rxPin, in
                 }
             break;
 #endif
-            default:
-                log_e("Bad UART Number");
-                return;
         }
     }