ALSA: hda/realtek - Fix a typo in model documentation

Some garbage was taken via copy-and-paste error.  Clean up.

Fixes: a26d96c7 ("ALSA: hda/realtek - Comprehensive model list for ALC259 & co")
Signed-off-by: Takashi Iwai <tiwai@suse.de>

Documentation/sound/hd-audio/models.rst

@@ -254,7 +254,7 @@ alc274-dell-aio
     ALC274 fixups on Dell AIO machines
 alc255-dummy-lineout
     Dell Precision 3930 fixups
-alc255-dell-headset"},
+alc255-dell-headset
     Dell Precision 3630 fixups
 alc295-hp-x360
     HP Spectre X360 fixups