because lsr may return less than the input buffer size, and the rest of the
audio code needs to know the new size.  This fixes the clicking that was
introduced with recent changes to the lsr code.  A huge thanks to remiss
for figuring this out.

git-svn-id: https://svn.musicpd.org/mpd/trunk@6273 09075e82-0dd4-0310-85a5-a0d7c8717e4f