avutil: use align == 0 for default alignment in audio sample buffer functions

Fixes: http://pad.lv/1264886, http://pad.lv/1241439
(cherry picked from commit 0109a09dc3850eb5dbff84a7bb50eb252a5a8f22)
Signed-off-by: Reinhard Tartler <siretart@tauware.de>

Conflicts:
	libavutil/avutil.h