PCI/AER: Fix rootport attribute paths in ABI docs

The 'aer_stats' directory never made it into the sixth and final revision
of the series adding the sysfs AER attributes.

Link: https://lore.kernel.org/r/20240202131635.11405-2-johan+linaro@kernel.org
Link: https://lore.kernel.org/lkml/20180621184822.GB14136@bhelgaas-glaptop.roam.corp.google.com/


Fixes: 12833017 ("PCI/AER: Add sysfs attributes for rootport cumulative stats")
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>