arm64: dts: rockchip: Drop 'rockchip,grf' prop from tsadc on rk3328

arm64: dts: rockchip: Drop 'rockchip,grf' prop from tsadc on rk3328

The 'rockchip,grf' property for tsadc in rk3328 wasn't actually used in
the driver and is no longer allowed in the DT since commit
e881662aa06a ("dt-bindings: thermal: rockchip: Tighten grf requirements")

So remove that property which fixes the following DT validation issue

  tsadc@ff250000 (rockchip,rk3328-tsadc): rockchip,grf: False schema does not allow [[58]]

Signed-off-by: Diederik de Haas <didi.debian@cknow.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>