ARM: mxc: time: add clk_prepare/clk_unprepare

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

arch/arm/plat-mxc/time.c

@@ -283,7 +283,7 @@ void __init mxc_timer_init(struct clk *timer_clk, void __iomem *base, int irq)
 {
 	uint32_t tctl_val;
 
-	clk_enable(timer_clk);
+	clk_prepare_enable(timer_clk);
 
 	timer_base = base;