p54usb: fix stalls caused by urb allocation failures

This patch squashes a few old bugs, which have been around since
the initial version of p54usb in one form or another.

we never freed a orphaned frame, when were denied the resources,
which are necessary to pass the data into the usb subsystem.
As a result we could end up with a full queue that wasn't emptied,
until the device was brought down.

Signed-off-by: Christian Lamparter <chunkeey@web.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>