EPERM means "Operation not permitted", which doesn't reflect the lack of
support for AER.  EPROTONOSUPPORT (Protocol not supported) is a better
choice of error code if the device or its root port lack support for AER.

Likewise, EINVAL means "Invalid argument", which is not suitable for cases
where the AER error device is missing or unusable.  ENODEV and
EPROTONOSUPPORT, respectively, fit better.
Suggested-by: NBorislav Petkov <bp@suse.de>
Signed-off-by: NJean Delvare <jdelvare@suse.de>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>
CC: Borislav Petkov <bp@suse.de>
CC: Prarit Bhargava <prarit@redhat.com>