usb-storage: support for more than 8 LUNs

This is necessary to make some storage arrays work.

Some storage devices have more than 8 LUNs. In addition
you can hook up a WideSCSI bus to USB. In these cases even
level 2 devices can have more than 8 LUNs. For them
it is necessary to simply believe the class specific
command and report its result back to the SCSI layer.

Off by one Alan noticed is fixed.

Signed-off-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>