PCI: pci.c: convert to use BUS_ATTR_RW

We are trying to get rid of BUS_ATTR() and the usage of that in pci.c
can be trivially converted to use BUS_ATTR_RW(), so use that instead.

Cc: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>