usb: dwc3: gadget: Check MPS of the request length

When preparing for SG, not all the entries are prepared at once. When
resume, don't use the remaining request length to calculate for MPS
alignment. Use the entire request->length to do that.

Cc: stable@vger.kernel.org
Fixes: 5d187c04 ("usb: dwc3: gadget: Don't setup more than requested")
Signed-off-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>