ASoC: wm8904: add new compatible string

The "wlf,wm8912" compatible string is used for wm8912, which
share driver with wm8904, however, the data type is different.

Signed-off-by: Bo Shen <voice.shen@atmel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/wm8904.txt

@@ -3,7 +3,7 @@ WM8904 audio CODEC
 This device supports I2C only.
 
 Required properties:
-  - compatible: "wlf,wm8904"
+  - compatible: "wlf,wm8904" or "wlf,wm8912"
   - reg: the I2C address of the device.
   - clock-names: "mclk"
   - clocks: reference to