clocksource/drivers/pistachio: Prevent ftrace recursion

Currently pistachio can be used as a scheduler clock. We properly marked
pistachio_read_sched_clock() as notrace but we then call another function
pistachio_clocksource_read_cycles() that _wasn't_ notrace.

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

Fix this by adding notrace attribute to the pistachio_clocksource_read_cycles()
function.
Signed-off-by: NJisheng Zhang <jszhang@marvell.com>
Signed-off-by: NDaniel Lezcano <daniel.lezcano@linaro.org>

drivers/clocksource/time-pistachio.c

@@ -67,7 +67,8 @@ static inline void gpt_writel(void __iomem *base, u32 value, u32 offset,
 	writel(value, base + 0x20 * gpt_id + offset);
 }
 
-static cycle_t pistachio_clocksource_read_cycles(struct clocksource *cs)
+static cycle_t notrace
+pistachio_clocksource_read_cycles(struct clocksource *cs)
 {
 	struct pistachio_clocksource *pcs = to_pistachio_clocksource(cs);
 	u32 counter, overflw;