drivers: uart: esp32: reset tx fifo during driver init

Resets uart tx fifo during driver initialization to have a well defined
initial condition mainly preventing unwanted characters being sent

Signed-off-by: Marcio Ribeiro <marcio.ribeiro@espressif.com>
diff --git a/drivers/serial/uart_esp32.c b/drivers/serial/uart_esp32.c
index b2d05e5..affcd08 100644
--- a/drivers/serial/uart_esp32.c
+++ b/drivers/serial/uart_esp32.c
@@ -276,6 +276,7 @@
 	uart_hal_set_rxfifo_full_thr(&data->hal, UART_RX_FIFO_THRESH);
 	uart_hal_set_txfifo_empty_thr(&data->hal, UART_TX_FIFO_THRESH);
 	uart_hal_rxfifo_rst(&data->hal);
+	uart_hal_txfifo_rst(&data->hal);
 
 	switch (cfg->parity) {
 	case UART_CFG_PARITY_NONE: