usb: dwc2: Avoid leaving the error_debugfs label unused

usb: dwc2: Avoid leaving the error_debugfs label unused

The error_debugfs label is only used when either
CONFIG_USB_DWC2_PERIPHERAL or CONFIG_USB_DWC2_DUAL_ROLE is enabled. Add
the same #if to the error_debugfs label itself as the code which uses
this label already has.

This avoids the following compiler warning:
  warning: label ‘error_debugfs’ defined but not used [-Wunused-label]

Fixes: e1c08cf23172ed ("usb: dwc2: Add missing cleanups when usb_add_gadget_udc() fails")
Acked-by: Minas Harutyunyan <Minas.Harutyunyan@synopsys.com>
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>