ALSA: ac97: Convert to RUNTIME_PM_OPS() macro

Use a newer RUNTIME_PM_OPS() macro instead of SET_RUNTIME_PM_OPS()
together with pm_ptr(), which makes CONFIG_PM ifdefs superfluous.

This optimizes slightly when CONFIG_PM is disabled, too.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://patch.msgid.link/20250313170731.26943-2-tiwai@suse.de