clocksource/drivers/timer-microchip-pit64b: Use 5MHz for clockevent

Use 5MHz clock for clockevent timers. This increases timer's
resolution.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20220304133601.2404086-4-claudiu.beznea@microchip.com


Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>