Some widespread USB interface chips with adaptive iso endpoints hang
after receiving a series of empty packets when they expect data.  This
completely disables audio playback on those devices.  To avoid this, we
have to send packets containing silence (zero samples) instead.

ALSA bug: http://bugtrack.alsa-project.org/alsa-bug/view.php?id=1585Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>