When bdl_pos_adj=0 is given, disable the position-check and the delayed
period update mechanism.  Usually bdl_pos_adj=0 is set only for the
debugging purpose on really broken hardwares.  It's better to disable
the extra complexity in such a case.
Signed-off-by: NTakashi Iwai <tiwai@suse.de>
Signed-off-by: NJaroslav Kysela <perex@perex.cz>