PCI: Remove duplicate check for positive return value from probe() functions

Function __pci_device_probe() tries to be careful about a PCI driver
probe() hook returning a positive value, but this is not really necessary,
since the same fix up is already done in local_pci_probe() (preceded by a
noisy warning), which renders this instance dead code.

Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.co.uk>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>