pcm: dmix_rewind corrupts application pointer fix

pcm: dmix_rewind corrupts application pointer fix

sometimes pulseaudio stops with the following assertion in libasound.so:
alsa-lib-1.0.29/src/pcm/pcm.c:2761:
snd_pcm_area_copy: Assertion `dst < src || dst >= src + bytes' failed.
Application pointer is handled properly, in cases of rewind operations.

Signed-off-by: Timo Wischer <twischer@de.adit-jv.com>
Signed-off-by: Ravikiran Polepalli <ravikiran_polepalli@mentor.com>
Signed-off-by: Mikhail Durnev <mikhail_durnev@mentor.com>
Signed-off-by: Mounesh Sutar <sutar.mounesh@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>