arm64: dts: allwinner: a64: pinetab: Fix cpvdd supply name

An older version of the analog codec binding referenced the headphone
amplifier binding as "hpvcc". However, by the time it was merged in
commit 21dd3020 ("ASoC: dt-bindings: sun50i-codec-analog: Add
headphone amp regulator supply"), the regulator reference was renamed to
"cpvdd". This board's device tree still uses the old name, which fails
to work at runtime, and which causes a warning from `make dtbs_check`.
Resolve both by fixing the name.

Fixes: 674ef1d0

 ("arm64: dts: allwinner: a64: add support for PineTab")
Signed-off-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>