ARM: mx31moboard: add clk_prepare/clk_unprepare

It's for migrating to generic clk framework API.
Signed-off-by: NRichard Zhao <richard.zhao@linaro.org>
Signed-off-by: NSascha Hauer <s.hauer@pengutronix.de>

arch/arm/mach-imx/mach-mx31moboard.c

@@ -507,7 +507,7 @@ static void mx31moboard_poweroff(void)
 	struct clk *clk = clk_get_sys("imx2-wdt.0", NULL);
 
 	if (!IS_ERR(clk))
-		clk_enable(clk);
+		clk_prepare_enable(clk);
 
 	mxc_iomux_mode(MX31_PIN_WATCHDOG_RST__WATCHDOG_RST);