ARM: mxs: use CLKSRC_OF helper to initialize timer

Select CLKSRC_OF and use clocksource_of_init() to initialize timer, so
that the call to mxs_timer_init() in clock driver can be removed.

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 4210204..fe2903d 100644
--- a/arch/arm/mach-mxs/timer.c
+++ b/arch/arm/mach-mxs/timer.c
@@ -242,18 +242,11 @@
 	return 0;
 }
 
-void __init mxs_timer_init(void)
+static void __init mxs_timer_init(struct device_node *np)
 {
-	struct device_node *np;
 	struct clk *timer_clk;
 	int irq;
 
-	np = of_find_compatible_node(NULL, NULL, "fsl,timrot");
-	if (!np) {
-		pr_err("%s: failed find timrot node\n", __func__);
-		return;
-	}
-
 	timer_clk = clk_get_sys("timrot", NULL);
 	if (IS_ERR(timer_clk)) {
 		pr_err("%s: failed to get clk\n", __func__);
@@ -304,3 +297,4 @@
 	irq = irq_of_parse_and_map(np, 0);
 	setup_irq(irq, &mxs_timer_irq);
 }
+CLOCKSOURCE_OF_DECLARE(mxs, "fsl,timrot", mxs_timer_init)