usb: dwc3: of-simple: fix use-after-free on remove

The clocks have already been explicitly disabled and put as part of
remove() so the runtime suspend callback must not be run when balancing
the runtime PM usage count before returning.

Fixes: 16adc674

 ("usb: dwc3: add generic OF glue layer")
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>