arm64: dts: allwinner: pinetab: Change regulator node name to avoid warning

The fixed regulator clock name has a unit address, but no reg property,
which generates a warning in DTC. Change its name to remove its useless
unit address.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Link: https://lore.kernel.org/r/20210901091852.479202-51-maxime@cerno.tech