usb: dwc2: pci: Fix an error code in probe

We added some error handling to this function but forgot to set the
error code on this path.

Fixes: ecd29dab ("usb: dwc2: pci: Handle error cleanup in probe")
Acked-by: Minas Harutyunyan <hminas@synopsys.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>