fix(uart): esp32/s2 baudrate > 1MHz

Fixes the baudrate for ESP32 and ESP32-S2 when the baud rate is higher than 1MHz.
REF_TICK is just 2MHZ and can handle up to 1MHZ baudrate.

Author: SuGlider

cores/esp32/esp32-hal-uart.c

@@ -508,10 +508,14 @@ uart_t *uartBegin(
 #if SOC_UART_SUPPORT_XTAL_CLK
   uart_config.source_clk = UART_SCLK_XTAL; // valid for C2, S3, C3, C6, H2 and P4
 #elif SOC_UART_SUPPORT_REF_TICK
-  uart_config.source_clk = UART_SCLK_REF_TICK; // valid for ESP32, S2
+  if (baudrate <= 1000000) {
+    uart_config.source_clk = UART_SCLK_REF_TICK; // valid for ESP32, S2 - MAX supported baud rate is 1MHz
+  } else {
+    uart_config.source_clk = UART_SCLK_APB; // baudrate may change with the APB Frequency!
+  }
 #else
   // Default CLK Source: CLK_APB for ESP32|S2|S3|C3 -- CLK_PLL_F40M for C2 -- CLK_PLL_F48M for H2 -- CLK_PLL_F80M for C6
-  uart_config.source_clk = UART_SCLK_DEFAULT; // baudrate may change with the CPU Frequency!
+  uart_config.source_clk = UART_SCLK_DEFAULT; // baudrate may change with the APB Frequency!
 #endif
 
   UART_MUTEX_LOCK();