tty: serial: samsung_tty: fix s3c24xx_serial_set_mctrl()

S3C2410_UCON is a 32bit register, so it must be read with rd_regl()
instead of rd_reg(), otherwise the upper bits will be zeroed. Fix this.

Fixes: 72a43046 ("tty: serial: samsung_tty: loopback mode support")
Tested-by: Chanho Park <chanho61.park@samsung.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Chanho Park <chanho61.park@samsung.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://lore.kernel.org/r/20220712140745.30362-1-m.szyprowski@samsung.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/samsung_tty.c

@@ -1018,7 +1018,7 @@ static unsigned int s3c24xx_serial_get_mctrl(struct uart_port *port)
 static void s3c24xx_serial_set_mctrl(struct uart_port *port, unsigned int mctrl)
 {
 	unsigned int umcon = rd_regl(port, S3C2410_UMCON);
-	unsigned int ucon = rd_reg(port, S3C2410_UCON);
+	unsigned int ucon = rd_regl(port, S3C2410_UCON);
 
 	if (mctrl & TIOCM_RTS)
 		umcon |= S3C2410_UMCOM_RTS_LOW;