arm64: dts: allwinner: h6: tanix-tx6: Fix regulator node names

Regulator node names don't reflect class of the device. Fix that by
prefixing names with "regulator-".

Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20210722161220.51181-2-jernej.skrabec@gmail.com