alps64: Fix for delay time for matrix scan

alps64: Fix for delay time for matrix scan

Delay less than 20us can cause false key detection in some situations.
With week internal pull-up takes time to charge stray capacitance of
trace between ground fill(and fingers), perhaps?

In particular, when testing Alps64 PCB without diodes tweezer is used
to close a key and this makes trace longer, more capacitance in result.