[qmi-usb] Remove usage of req->node

With the recent changes to usb stack, each driver in the usb stack has its own list_node_t*
so as to avoid stamping on other driver's lists. This changeset removes
usage of req->node in qmi-usb-transport

Test:fx full-build with req->node commented.

Change-Id: I1de091479dd549d019d997ca792a8fad32cd4c25
1 file changed