ALSA: intel-hdmi-audio: Convert to SYSTEM_SLEEP_PM_OPS()

Use the newer SYSTEM_SLEEP_PM_OPS() macro instead of
SET_SYSTEM_SLEEP_PM_OPS() together with pm_ptr(), which allows us
dropping ugly __maybe_unused attributes.

This optimizes slightly	when CONFIG_PM is disabled, too.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://patch.msgid.link/20250313170731.26943-10-tiwai@suse.de