ASoC: soc-core: Remove unused 'ret' variable

commit 9bde4f0b (ASoC: core: Fix SOC_DOUBLE_RANGE() macros) introduced
the following build warning:

sound/soc/soc-core.c:2999:6: warning: unused variable 'ret' [-Wunused-variable]

Remove the unused 'ret' variable.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>