usb: gadget: net2280: restore ep_cfg after defect7374 workaround

Defect 7374 workaround enables all GPEP as endpoint 0. Restore
endpoint number when defect 7374 workaround is disabled. Otherwise,
check to match USB endpoint number to hardware endpoint number in
net2280_enable() fails.

Cc: <stable@vger.kernel.org> # 4.2
Reported-by: Paul Jones <p.jones@teclyn.com>
Signed-off-by: Mian Yousaf Kaukab <yousaf.kaukab@intel.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>