MAINTAINERS: Add arch/x86/kernel/quirks.c to PCI file patterns

I'm not asserting any claim over arch/x86/kernel/quirks.c, and I don't plan
to merge changes to it, but some of the quirks there are PCI-related, and
I'd like to see changes to them.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>