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: NJisheng Zhang <jszhang@marvell.com>
Signed-off-by: NDaniel Lezcano <daniel.lezcano@linaro.org>

drivers/clocksource/fsl_ftm_timer.c

@@ -118,7 +118,7 @@ static inline void ftm_reset_counter(void __iomem *base)
 	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);
 }