clocksource/drivers/timer-microchip-pit64b: Use notrace

clocksource/drivers/timer-microchip-pit64b: Use notrace

Use notrace for mchp_pit64b_sched_read_clk() to avoid recursive call of
prepare_ftrace_return() when issuing:
echo function_graph > /sys/kernel/debug/tracing/current_tracer

Fixes: 625022a5f160 ("clocksource/drivers/timer-microchip-pit64b: Add Microchip PIT64B support")
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20220304133601.2404086-3-claudiu.beznea@microchip.com
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>