ASoC: dt-bindings: mt8192-mt6359: fix typo in the example

Both driver "sound/soc/mediatek/mt8192/mt8192-mt6359-rt1015-rt5682.c"
and DT binding property use underscore version compatible string.

Fixes the typo in the example.
Signed-off-by: Tzung-Bi Shih <tzungbi@google.com>
Link: https://lore.kernel.org/r/20201201132614.1691352-5-tzungbi@google.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/mt8192-mt6359-rt1015-rt5682.yaml

@@ -31,7 +31,7 @@ examples:
   - |
 
     sound: mt8192-sound {
-        compatible = "mediatek,mt8192-mt6359-rt1015-rt5682";
+        compatible = "mediatek,mt8192_mt6359_rt1015_rt5682";
         mediatek,platform = <&afe>;
         pinctrl-names = "aud_clk_mosi_off",
                         "aud_clk_mosi_on";