PCI: aer_inject: Fix return values when device not found

Currently the aer_inject driver returns -ENOTTY when the target PCIe
device root port is not found or if the device or root port doesn't
support AER.

In the case where the root port isn't found, the driver should return
-ENODEV, and in the other cases it should return -EPERM.

Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>