ARM: dt: sunxi: Remove i2c controller clock-frequency that matches default

The clock-frequency values of the i2c controller nodes match the
defaults of the driver. Remove the properties to use the defaults,
and be consistent with sun8i.

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