ARM: mxs: look up timrot clock from device tree

Change call clk_get_sys() to of_clk_get() to look up timrot clock from
device tree, so that the clk_register_clkdev() call for timrot can be
saved in clock driver.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
diff --git a/arch/arm/mach-mxs/timer.c b/arch/arm/mach-mxs/timer.c
index fe2903d..f5142aa 100644
--- a/arch/arm/mach-mxs/timer.c
+++ b/arch/arm/mach-mxs/timer.c
@@ -247,7 +247,7 @@
 	struct clk *timer_clk;
 	int irq;
 
-	timer_clk = clk_get_sys("timrot", NULL);
+	timer_clk = of_clk_get(np, 0);
 	if (IS_ERR(timer_clk)) {
 		pr_err("%s: failed to get clk\n", __func__);
 		return;