ASoC: tegra: tegra210_ahub: Fix compile warning with CONFIG_PM=n

ASoC: tegra: tegra210_ahub: Fix compile warning with CONFIG_PM=n

Fix trivial compile warnings wrt unused functions by adding
__maybe_unused prefix:
  sound/soc/tegra/tegra210_ahub.c:567:12: warning: 'tegra_ahub_runtime_suspend' defined but not used [-Wunused-function]
  sound/soc/tegra/tegra210_ahub.c:579:12: warning: 'tegra_ahub_runtime_resume' defined but not used [-Wunused-function]

Fixes: 16e1bcc2caf4 ("ASoC: tegra: Add Tegra210 based AHUB driver")
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20200803141850.23713-4-tiwai@suse.de
Signed-off-by: Mark Brown <broonie@kernel.org>