ASoC: Remove volatility from WM8900 POWER1 register

Not all bits can be read back from POWER1 so avoid corruption when using
a read/modify/write cycle by marking it non-volatile - the only thing we
read back from it is the chip revision which has diagnostic value only.
We can re-add later but that's a more invasive change than is suitable
for a bugfix.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Cc: stable@kernel.org

sound/soc/codecs/wm8900.c

@@ -186,7 +186,6 @@ static int wm8900_volatile_register(unsigned int reg)
 {
 	switch (reg) {
 	case WM8900_REG_ID:
-	case WM8900_REG_POWER1:
 		return 1;
 	default:
 		return 0;
@@ -1200,11 +1199,6 @@ static int wm8900_probe(struct snd_soc_codec *codec)
 		return -ENODEV;
 	}
 
-	/* Read back from the chip */
-	reg = snd_soc_read(codec, WM8900_REG_POWER1);
-	reg = (reg >> 12) & 0xf;
-	dev_info(codec->dev, "WM8900 revision %d\n", reg);
-
 	wm8900_reset(codec);
 
 	/* Turn the chip on */