ARM: dts: sun6i: hummingbird: Fix VDD-CPU and VDD-GPU regulator names

The VDD-CPU and VDD-GPU regulators were incorrectly swapped.

Fixes: bab03561

 ("ARM: dts: sun6i: hummingbird: Add AXP221 regulator
       nodes")

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