ALSA: ASoC: Fix typo in snd_soc_card update documentation

Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>

Documentation/sound/alsa/soc/machine.txt

@@ -9,7 +9,7 @@ the audio subsystem with the kernel as a platform device and is represented by
 the following struct:-
 
 /* SoC machine */
-struct snd_soc_card {_
+struct snd_soc_card {
 	char *name;
 
 	int (*probe)(struct platform_device *pdev);