PCI: Constify bin_attribute structures

Add const to bin_attribute structures as they are only passed to the
functions sysfs_{remove/create}_bin_file. The corresponding arguments are
of type const, so declare the structures to be const.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>