ALSA: hda - Add mono speaker quirk for Dell Inspiron 5439

commit eb82594b75b0cf54c667189e061934b7c49b5d42 upstream.

This machine also has mono output if run through DAC node 0x03.

BugLink: https://bugs.launchpad.net/bugs/1256212


Tested-by: David Chen <david.chen@canonical.com>
Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>