usb: wusbcore: fix short transfers

If a URB is broken up into multiple transfer segments and a short
transfer occurs in any segment other than the last, the URB will
currently get stuck in the driver forever.  This patch adds a check for
a short transfer and cleans up any pending segments so the URB can
complete properly.

Signed-off-by: Thomas Pugliese <thomas.pugliese@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>