usb: gadget: composite: Update usb_core_id with composite driver

Currently composite_template_driver is being used statically and
it doesn't update usb_core_id passed from gadget driver assuming
that there is always one gadget binding with one udc driver. For
multiple gadget drivers using different udc driver it is required
to use usb_core_id to bind between composite gadget driver and
udc driver. Hence update gadget driver with usb core id before
registering it.

Change-Id: I9f903dba070b5a1a54a072d98a522442afb2db2a
Signed-off-by: Mayank Rana <mrana@codeaurora.org>