ALSA: core: update comment on snd_card.controls_rwsem

Since commit 5bbb1ab5 ("control: use counting semaphore as write lock
for ELEM_WRITE operation"), this has been locking the controls including
their values, not just the list of controls.

Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Link: https://lore.kernel.org/r/20230428095941.1706278-6-oswald.buddenhagen@gmx.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>