ALSA: emu10k1: remove now superfluous mixer locking

ALSA: emu10k1: remove now superfluous mixer locking

Since commit 5bbb1ab5bd ("control: use counting semaphore as write lock
for ELEM_WRITE operation"), mixer values have been fully read-write
locked. This means that it is now unnecessary to apply any additional
locks to values that are accessed solely by mixer callbacks. Values that
are read outside mixer callbacks still need write locking. There are no
cases of mixer values being written outside mixer callbacks, so no read
locks remain in mixer callbacks.

Note that the removed locks refer only to the emu data structure, not
the card's registers as the lock's name suggests.

Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Link: https://lore.kernel.org/r/20230428095941.1706278-7-oswald.buddenhagen@gmx.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>