[ALSA] sound: patch_sigmatel.c fix shadowed variable warning

Temp variable in the loop shadows the second argument (which is otherwise
unused in this function).  Change this to defcfg as it is used to hold
the default config.
sound/pci/hda/patch_sigmatel.c:2759:18: warning: symbol 'cfg' shadows an earlier one
sound/pci/hda/patch_sigmatel.c:2734:26: originally declared here

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>