usb: wusbcore: combine iso transfer result frame reads when possible

When reading the transfer result data for an isochronous in request, if
the current frame actual_length is contiguous with the next frame and
actual_length is a multiple of the DTI endpoint max packet size, combine
the current frame with the next frame in a single URB.  This reduces the
number of URBs that must be submitted in that case which increases
performance and reduces CPU interrupt overhead.

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