usb: dwc3: gadget: Check MaxPacketSize from descriptor

endpoint->maxpacket is not updated after setting the
usb_set_maxpacket_limit() on endpoint enable. The MaxPacketSize can be
different than the endpoint->maxpacket_limit.

DWC3 has been consistently using MaxPacketSize from the endpoint's
descriptor, so let's keep it consistent and use the MaxPacketSize from
the endpoint's descriptor instead.

Signed-off-by: Thinh Nguyen <thinhn@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>