arm64: dts: allwinner: h5: Fix GPU thermal zone node name

The GPU thermal zone is named gpu_thermal. However, the underscore is
an invalid character for a node name and the thermal zone binding
explicitly requires that zones are called *-thermal. Let's fix it.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Link: https://lore.kernel.org/r/20210901091852.479202-48-maxime@cerno.tech