docs: pci: fix broken links due to conversion from pci.txt to pci.rst

Some documentation files were still pointing to the old place.

Fixes: 229b4e07 ("Documentation: PCI: convert pci.txt to reST")
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Paul E. McKenney <paulmck@linux.ibm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>