clocksource/drivers/tegra: Minor code clean up

Correct typo and use proper upper casing for acronyms in the comments,
use common style for error messages, prepend error messages with
"tegra-timer:", add error message for cpuhp_setup_state() failure and
clean up whitespaces in the code to fix checkpatch warnings.

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>