USB: interface PM state

This patch (as880) strives to keep the PM core's idea of a USB
interface's power state in synch with usbcore's own idea.  In the end
this doesn't really matter, but it's better to be consistent.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>