ASoC: wm8731: Use the preferred form for passing a size of a struct

According to Documentation/CodingStyle - Chapter 14:

"The preferred form for passing a size of a struct is the following:

	p = kmalloc(sizeof(*p), ...);

The alternative form where struct name is spelled out hurts readability and
introduces an opportunity for a bug when the pointer variable type is changed
but the corresponding sizeof that is passed to a memory allocator is not."

So do it as recommeded.

Cc: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/wm8731.c

@@ -680,8 +680,7 @@ static int wm8731_spi_probe(struct spi_device *spi)
 	struct wm8731_priv *wm8731;
 	int ret;
 
-	wm8731 = devm_kzalloc(&spi->dev, sizeof(struct wm8731_priv),
-			      GFP_KERNEL);
+	wm8731 = devm_kzalloc(&spi->dev, sizeof(*wm8731), GFP_KERNEL);
 	if (wm8731 == NULL)
 		return -ENOMEM;