Change default baud rate back to 74906bps, compatible with boot ROM rate

This reverts a behaviour change from 3ceadfc0a6.

examples/tests/hmac_test_vectors/hmac_test_vectors.c

@@ -8,7 +8,7 @@
  * This sample code is in the public domain.,
  */
 #include "espressif/esp_common.h"
-#include "espressif/sdk_private.h"
+#include "esp/uart.h"
 #include "FreeRTOS.h"
 #include "mbedtls/md.h"
 
@@ -130,7 +130,7 @@ static void test_md5(void)
 
 void user_init(void)
 {
-    sdk_uart_div_modify(0, UART_CLK_FREQ / 115200);
+    uart_set_baud(0, 115200);
 
     test_md5();