/proc/bus/pci allows you to mmap resource ranges too, so we should probably be
checking to make sure the mapping is somewhat valid.  Uses the same code as the recent sysfs mmap range checking patch from Linus.
Acked-by: NDavid Miller <davem@davemloft.net>
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>