ANDROID: db845c: add mux-core.ko module

Since commit eec611d2 ("ASoC: codecs: wcd938x: add mux control
support for hp audio mux") the core MULTIPLEXER module is selected via
CONFIG_SND_SOC_WCD938X. Add the mux-core.ko module to the db845c list.

Fixes: eec611d2 ("ASoC: codecs: wcd938x: add mux control support for hp audio mux")
Change-Id: I4e1cec4320e0c442ccb6c653b2ab0f9321909926
Signed-off-by: Carlos Llamas <cmllamas@google.com>