usb: gadget: eem: fix echo command packet response issue

usb: gadget: eem: fix echo command packet response issue

when receive eem echo command, it will send a response,
but queue this response to the usb request which allocate
from gadget device endpoint zero,
and transmit the request to IN endpoint of eem interface.

on dwc3 gadget, it will trigger following warning in function
__dwc3_gadget_ep_queue(),

	if (WARN(req->dep != dep, "request %pK belongs to '%s'\n",
				&req->request, req->dep->name))
		return -EINVAL;

fix it by allocating a usb request from IN endpoint of eem interface,
and transmit the usb request to same IN endpoint of eem interface.

Signed-off-by: Linyu Yuan <linyyuan@codeaurora.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20210616115142.34075-1-linyyuan@codeaurora.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>