We can simplify the code gracefully with new guard() macro and co for
automatic cleanup of locks.

A couple of functions that use snd_card_ref() and *_unref() are also
cleaned up with a defined class, too.

Only the code refactoring, and no functional changes.
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20240227085306.9764-25-tiwai@suse.de