ARM: dts: sun8i: a23/a33: Fix up RTC device node

The RTC module on the A23 was claimed to be the same as on the A31, when
in fact it is not. The A31 does not have an RTC external clock output,
and its internal RC oscillator's average clock rate is not in the same
range. The A33's RTC is the same as the A23.

This patch fixes the compatible string and clock properties to conform
to the updated bindings. The register range is also fixed.

Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>