Add missing CONFIG_SND_SOC_AN7581 symbol.
Fix error:
------------------------------------------------------------------
ASoC support for Airoha AN7581 chip (SND_SOC_AN7581) [N/m/?] (NEW)
make[7]: *** [scripts/kconfig/Makefile:85: syncconfig] Error 1
------------------------------------------------------------------
Fixes: 2566781 ("airoha: an7583: remove source-only flag")
Signed-off-by: Mikhail Zhilkin <csharper2005@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/24285
Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>