This sets urb->interval in two places it hadn't previously been set,
allowing things like SOX and XMMS to play through usb audio.

Using this and the previous patches, I was able to verify playback
of some Ogg Vorbis encoded music using most of the 2.5.17 host
controller drivers.  However, "uhci-hcd" and "usb-uhci-hcd" did
not want to bind the audio driver:  reading the config descriptor
(in audio.c) stalled rather consistently.  That failure was seen
with the other USB 1.1 drivers too, but not as consistently.