docs: PCI: Fix typos

Fix typos in PCI docs.

Link: https://lore.kernel.org/r/20231223184720.25645-1-tintinm2017@gmail.com
Link: https://lore.kernel.org/r/20231223184412.25598-1-tintinm2017@gmail.com
Signed-off-by: Attreyee Mukherjee <tintinm2017@gmail.com>
[bhelgaas: squashed, commit log]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>  # for "busses" only