pci: use security_capable() when checking capablities during config space read

Eric Paris noted that commit de139a3 ("pci: check caps from sysfs file
open to read device dependent config space") caused the capability check
to bypass security modules and potentially auditing.  Rectify this by
calling security_capable() when checking the open file's capabilities
for config space reads.

Reported-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: James Morris <jmorris@namei.org>