pcie: minor cleanups for slot control/status

Rename function arguments to make intent clearer.
Better documentation for slot control logic.

Suggested-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
2 files changed