DragonFlyBSD

this fixes a "pcm0:virtual:0:dsp0.2: play interrupt timeout, channel dead" error
and sound breaking off after a few seconds of playback I encountered on my
Thinkpad X40. It was discussed on freebsd-current in 2004¹ but that code is no
longer present in FreeBSD while we still have it.

The patch² removes a line fixing a channel timeout to 1 tick instead of the
value calculated immediately beforehand, thus restoring the calculation.

[1] http://lists.freebsd.org/pipermail/freebsd-current/2004-
September/036805.html
[2]
http://gitweb.dragonflybsd.org/~matthiasr/dragonfly.git/commitdiff/4d3f6d0ed3435
46cbd7c8cfeaf0cce3f449122b6