arm64: dts: mt8173: Fix auxadc node

The devicetree node for mt8173-auxadc lacks the clock and
io-channel-cells property. This leads to a non-working driver.

	mt6577-auxadc 11001000.auxadc: failed to get auxadc clock
	mt6577-auxadc: probe of 11001000.auxadc failed with error -2

Fix these fields to get the device up and running.

Fixes: 748c7d4d ("ARM64: dts: mt8173: Add thermal/auxadc device
nodes")
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>