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

When applying commit 7d26b587 (fix failure path in
dwc3_pci_probe()), I mistakenly left out one of the
possible failures where we would return success even
on the error case.

This patch fixes that mistake.

Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>