ASoC: 88pm860x: Don't change pm860x->dir setting if pm860x_set_dai_sysclk fails

88pm860x does not support slave mode, so it returns -EINVAL for
PM860X_CLK_DIR_IN. Current code changes pm860x->dir setting before
return error, so it has impact on the logic of pm860x_pcm_set_dai_fmt.

This patch adds comment for the reason to return -EINVAL for
PM860X_CLK_DIR_IN, and avoid changing pm860x->dir setting if
pm860x_set_dai_sysclk fails.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Haojian Zhuang <haojian.zhuang@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>