arm64: dts: allwinner: h5: Fix PMU compatible

The commit c35a516a ("arm64: dts: allwinner: H5: Add PMU node")
introduced support for the PMU found on the Allwinner H5. However, the
binding only allows for a single compatible, while the patch was adding
two.

Make sure we follow the binding.

Fixes: c35a516a ("arm64: dts: allwinner: H5: Add PMU node")
Signed-off-by: Maxime Ripard <maxime@cerno.tech>