round the result up to a multiple of 4 bytes so that it will always
be a multiple of the sample size. Also use the actual buffer size
from sc->bufsz instead of the default DS1_BUFFSIZE.
This fixes panics and bad distortion I have seen on Yamaha DS-1
hardware, mainly when playing certain Real Audio media.
Reviewed by: orion (an earlier version of the patch)
3944d0ff35