ASoC: wm8776: Add WM8775 device ID to the WM8776

The WM8775 is register compatible with the WM8776 so can be supported with
the same driver though it is an ADC only part. Add the device ID to the
WM8776 driver, further updates will be added in the future.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>