usb: musb: dsps: don't fake of_node to musb core

If we pass our own of_node to musb_core, at least
pinctrl settings will be duplicated, meaning that
pinctrl framework will try to select default pin
state for musb_core when they were already requested
by musb-dsps.

A Warning will be printed however things will still
work.

Reported-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>