fix warning "control reaches end of non-void function"

Add a return 0 analogous to uart_mxc_port[0-2]_exit.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Holger Schurig <hs4233@mail.mn-solutions.de>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Martin Fuzzey <mfuzzey@gmail.com>

arch/arm/mach-mx2/mx27ads.c

@@ -135,6 +135,7 @@ static int uart_mxc_port3_exit(struct platform_device *pdev)
 {
 	mxc_gpio_release_multiple_pins(mxc_uart3_pins,
 			ARRAY_SIZE(mxc_uart3_pins));
+	return 0;
 }
 
 static int mxc_uart4_pins[] = {