watchdog: sunxi: Change compatibles

The Allwinner A10 and A31 compatibles were following a slightly different
compatible patterns than the rest of the SoCs for historical reasons. Change
the compatibles to match the other pattern in the watchdog controller driver
for consistency.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>