Hide IME when switching to Radial Time Picker

When switching back to the Radial Time Picker with an
IME visible, make sure to hide it.

Test: Set time from Settings. Switch to TextInputTimePicker.
      Enter text so IME appears.  Switch back to RadialTimePicker
      IME should be hidden again.

Change-Id: Ia0ed149d74333b2f643d50a324172b64aa5e223b