ARM: dts: sun7i: include correct ccu clock header

Including sun4i header instead of sun7i prevents using sun7i specific
defines.

Substitute header inclusion in sun7i-a20.dtsi using right one.

Signed-off-by: Giulio Benetti <giulio.benetti@micronovasrl.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>