ALSA: HDA: Fix master control for Cirrus Logic 421X

The control name "HP/Speakers" is non-standard, and since there is
only one DAC on this chip there is no need for a virtual master
anyway.

Cc: stable@kernel.org
Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>