PCI/AER: Update aer-inject URL

The link to the aer-inject referenced leads to an empty repo and seems no
longer used. Replace it with the link mentioned in
Documentation/PCI/pcieaer-howto.rst.

Link: https://lore.kernel.org/r/20220115104921.21606-1-yangyicong@hisilicon.com


Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>