PCI: Kconfig help: don't refer to the PCI-HOWTO

A HOWTO that hasn't been updated for half a dozen years no longer
"contains valuable information about which PCI hardware does work under
Linux and which doesn't".

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>