ASoC: sigmadsp: Simplify with snd_ctl_activate_id()

Use the standard snd_ctl_activate_id() helper instead of an open code
for code simplification.

Acked-by: Mark Brown <broonie@kernel.org>
Cc: Lars-Peter Clausen <lars@metafoo.de>
Cc: "Nuno Sá" <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20230718141304.1032-7-tiwai@suse.de


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