fix(uart): missing class qualifier declaration

Author: SuGlider

cores/esp32/HardwareSerial.cpp

@@ -617,7 +617,7 @@ bool HardwareSerial::setMode(SerialMode mode) {
 // UART_CLK_SRC_REF_TICK     :: ESP32 and ESP32-S2
 // Note: CLK_SRC_PLL Freq depends on the SoC - ESP32-C2 has 40MHz, ESP32-H2 has 48MHz and ESP32-C5, C6, C61 and P4 has 80MHz
 // Note: ESP32-C6, C61, ESP32-P4 and ESP32-C5 have LP UART that will use only RTC_FAST or XTAL/2 as Clock Source
-bool setClockSource(SerialClkSrc clkSrc) {
+bool HardwareSerial::setClockSource(SerialClkSrc clkSrc) {
   return uartSetClockSource(_uart, (uart_sclk_t) clkSrc);
 }