ASoC: cs43130: Fix unused compiler warnings for PM runtime

Add __maybe_unused prefix for addressing the following warnings:
  sound/soc/codecs/cs43130.c:2615:12: warning: ‘cs43130_runtime_resume’ defined but not used [-Wunused-function]
  sound/soc/codecs/cs43130.c:2596:12: warning: ‘cs43130_runtime_suspend’ defined but not used [-Wunused-function]

Fixes: 8f1e5bf9 ("ASoC: cs43130: Add support for CS43130 codec")
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Mark Brown <broonie@kernel.org>