ALSA: ASoC - Add missing __devexit annotation to wm8350.c

Added the missing __devexit annotation to wm8350_codec_remove():
  sound/soc/codecs/wm8350.c:1546: warning: 'wm8350_codec_remove' defined but not used

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