Previously pcie_device_init() called get_device() if device_register() for
the new pcie_device succeeded, and remove_iter() called put_device() when
removing before unregistering the device.

But device_register() already increments the reference count in
device_add(), so we don't need to do it again here.
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>