[ALSA] hda-codec - Feed front signals to all surrounds

HDA Codec driver
Feed front signals to all surround channels if no data is given
for surround channels.

It seems that CLFE works as expected (only center outputs) even if
connected from the front line - at least on my test system.
If this change causes problems on other system (e.g. only the left
channel is transferred to the center channel), please let me know...

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