ALSA: hda - Fixing background noise on Dell Inspiron 3162

After login to the desktop on Dell Inspiron 3162,
there's a very loud background noise comes from the builtin speaker.
The noise does not go away even if the speaker is muted.

The noise disappears after using the aamix fixup.

Codec: Realtek ALC3234
Address: 0
AFG Function Id: 0x1 (unsol 1)
    Vendor Id: 0x10ec0255
    Subsystem Id: 0x10280725
    Revision Id: 0x100002
    No Modem Function Group found

BugLink: http://bugs.launchpad.net/bugs/1549620
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>