clocksource/drivers/oxnas: Fix OX820 compatible

The OX820 compatible is wrong is the driver, fix it.

Fixes: 2ea3401e ("clocksource/drivers/oxnas: Add OX820 compatible")
Reported-by: Daniel Golle <daniel@makrotopia.org>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>