[ALSA] hda-codec - code cleanups in patch_sigmatel.c

Clean up the mixer entries for Input Source using a macro.

Signed-off-by: Maxim Levitsky <maximlevitsky@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>