usb: musb: fix incorrect usage of resource pointer

We can't simply pass the resource pointer from our
device down to our children, otherwise module
reinsertion will not work as the resource will
continue to be marked as busy.

Fix it by building a proper struct resource for
our child musb device.

Tested-by: Dmitry Lifshitz <lifshitz@compulab.co.il>
Signed-off-by: Felipe Balbi <balbi@ti.com>