ALSA: HDA: Use LPIB Position fix for Intel SCH Poulsbo

Several people with this chipset have reported inconsistent/sloppy
values for position reporting when the DMA position buffer is used,
and that setting position_fix=1 have fixed their problems.

BugLink: https://bugs.launchpad.net/bugs/825709
Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>