ASoC: core: use PTR_ERR instead of PTR_RET

PTR_RET is deprecated. PTR_ERR_OR_ZERO should be used instead. However,
we already know that IS_ERR is true, and thus PTR_ERR_OR_ZERO would
never yield zero, so we can use PTR_ERR here.

Signed-off-by: Christoph Jaeger <christophjaeger@linux.com>
Signed-off-by: Mark Brown <broonie@linaro.org>