USB: usb-storage: merge CB and CBI transport routines

This patch (as1173) merges usb-storage's CB and CBI transports into a
single routine.  So much of their code is common, it's silly to keep
them separate.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: Matthew Dharm <mdharm-usb@one-eyed-alien.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>