usb: dwc3: pci: fix failure path in dwc3_pci_probe()

dwc3_pci_probe() would return success even if the calls to
dwc3_get_device_id() or platform_device_alloc() fail, fix that.

Signed-off-by: Paul Zimmerman <paulz@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>