staging: dwc2: remove some device-mode related debug code

This code appears to be partially incorrect. Since this is only debug
code and only applies to device mode, it seems better to remove this
code for now than to invest time fixing it.

Signed-off-by: Matthijs Kooijman <matthijs@stdin.nl>
Acked-by: Paul Zimmerman <paulz@synopsys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>