mfd: wcd9xxx: use codec device id to register the device.

The current code registers multiple devices for i2c clients. This
results in code repetition. instead its better to register single
i2c client and register codec based on device id.

Change-Id: Ifb4adbd47b7a2bf7d32be637fd0641545cd84286
Signed-off-by: Asish Bhattacharya <asishb@codeaurora.org>