ALSA: sound/atmel/ac97c.c: remove unused variable

The recently added DT support for the ac97 driver is causing
a gcc warning:

sound/atmel/ac97c.c: In function 'atmel_ac97c_probe_dt':
sound/atmel/ac97c.c:919:29: warning: unused variable 'match' [-Wunused-variable]
  const struct of_device_id *match;

The variable is clearly unused, so we can remove it.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Alexander Stein <alexanders83@web.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>