include/console/uart: make index parameter unsigned

The UART index is never negative, so make it unsigned and drop the
checks for the index to be non-negative.

Change-Id: I64bd60bd2a3b82552cb3ac6524792b9ac6c09a94
Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/45294
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/soc/mediatek/common/uart.c

@@ -139,22 +139,22 @@ static int mtk_uart_tst_byte(void)
 	return (read8(&uart_ptr->lsr) & UART8250_LSR_DR) == UART8250_LSR_DR;
 }
 
-void uart_init(int idx)
+void uart_init(unsigned int idx)
 {
 	mtk_uart_init();
 }
 
-unsigned char uart_rx_byte(int idx)
+unsigned char uart_rx_byte(unsigned int idx)
 {
 	return mtk_uart_rx_byte();
 }
 
-void uart_tx_byte(int idx, unsigned char data)
+void uart_tx_byte(unsigned int idx, unsigned char data)
 {
 	mtk_uart_tx_byte(data);
 }
 
-void uart_tx_flush(int idx)
+void uart_tx_flush(unsigned int idx)
 {
 	mtk_uart_tx_flush();
 }