ASoC: wm8904: Make undocumented registers non-readable

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Reviewed-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/wm8904.c

@@ -312,7 +312,7 @@ static bool wm8904_readable_register(struct device *dev, unsigned int reg)
 	case WM8904_FLL_NCO_TEST_1:
 		return true;
 	default:
-		return true;
+		return false;
 	}
 }