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>
diff --git a/arch/arm/plat-mxc/time.c b/arch/arm/plat-mxc/time.c
index 1c96cdb..7daf7c9 100644
--- a/arch/arm/plat-mxc/time.c
+++ b/arch/arm/plat-mxc/time.c
@@ -283,7 +283,7 @@
 {
 	uint32_t tctl_val;
 
-	clk_enable(timer_clk);
+	clk_prepare_enable(timer_clk);
 
 	timer_base = base;