PCI: Tidy comments

Make comments follow multi-line comment conventions. No functional change
intended.

Link: https://lore.kernel.org/r/YUZJenW2UCA4Qu0O@pranay-desktop


Signed-off-by: Pranay Sanghai <pranaysanghai@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>