ALSA: aloop: Constify ops structs

ALSA: aloop: Constify ops structs

The only usage of the ops field in the loopback_cable struct is to call
its members, the field it self is never changed. Make it a pointer to
const. This allows us to constify two static loopback_ops structs to
allow the compiler to put them in read-only memory.

Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Link: https://lore.kernel.org/r/20201120231046.76758-1-rikard.falkeborn@gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>