ALSA: HDA: Use one dmic only for Dell Studio 1558

There are no signs of a dmic at node 0x0b, so the user is left with
an additional internal mic which does not exist. This commit removes
that non-existing mic.

Cc: stable@kernel.org (2.6.32+)
BugLink: http://bugs.launchpad.net/bugs/731706
Reported-by: James Page <james.page@canonical.com>
Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>