ASoC: Fix compile warning in wm8750.c

sound/soc/codecs/wm8750.c:784:2: warning: missing braces around initializer
sound/soc/codecs/wm8750.c:784:2: warning: (near initialization for ‘wm8750_spi_ids[2].name’)

It's because struct spi_device_id.name is a char array, not a pointer,
while the driver initializes explicitly with 0.

Signed-off-by: Takashi Iwai <tiwai@suse.de>