usb: gadget: net2280: reset sequence number on ep enable

Sequence number can be out of sync if endpoint is disabled after some
data transfers and enabled again. Reset it to stay in sync with host.

Tested-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Mian Yousaf Kaukab <yousaf.kaukab@intel.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>