clocksource/drivers/tegra: Reset hardware state on init

Reset timer's hardware state to ensure that initially it is in a
predictable state.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-By: Peter De Schrijver <pdeschrijver@nvidia.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>