clocksource/drivers/fsl_ftm_timer: Prevent ftrace recursion

Having a traceable function in the sched_clock() path leads to a recursion
within ftrace and a kernel crash.

We should not trace the ftm_read_sched_clock() function.

Fix this by adding the notrace attribute to this function.

Signed-off-by: Jisheng Zhang <jszhang@marvell.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
diff --git a/drivers/clocksource/fsl_ftm_timer.c b/drivers/clocksource/fsl_ftm_timer.c
index ef43469..10202f1 100644
--- a/drivers/clocksource/fsl_ftm_timer.c
+++ b/drivers/clocksource/fsl_ftm_timer.c
@@ -118,7 +118,7 @@
 	ftm_writel(0x00, base + FTM_CNT);
 }
 
-static u64 ftm_read_sched_clock(void)
+static u64 notrace ftm_read_sched_clock(void)
 {
 	return ftm_readl(priv->clksrc_base + FTM_CNT);
 }