ALSA: x86: mark hdmi suspend/resume functions as __maybe_unused
The two functions are unused when CONFIG_PM_SLEEP is disabled:
sound/x86/intel_hdmi_audio.c:1633:12: error: 'hdmi_lpe_audio_resume' defined but not used [-Werror=unused-function]
sound/x86/intel_hdmi_audio.c:1622:12: error: 'hdmi_lpe_audio_suspend' defined but not used [-Werror=unused-function]
Marking them as __maybe_unused avoids the warning without introducing an
ugly #ifdef.