PCI/AER: Log aer_inject error injections

Log successful error injections so that injected errors can be
differentiated from real errors.

Suggested-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: Borislav Petkov <bp@suse.de>