ASoC: wm9712: fix unused variable warning

The 'ret' variable is now only used in an #ifdef, and causes a
warning if it is declared outside of that block:

sound/soc/codecs/wm9712.c: In function 'wm9712_soc_probe':
sound/soc/codecs/wm9712.c:641:6: error: unused variable 'ret' [-Werror=unused-variable]

Fixes: 2ed1a8e0 ("ASoC: wm9712: add ac97 new bus support")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>