scsi: usb: uas: Declare two host templates and host template pointers const

Improve source code documentation by constifying host templates that are
not modified.

Acked-by: Alan Stern <stern@rowland.harvard.edu> (for usb-storage)
Acked-by: Oliver Neukum <oneukum@suse.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Oliver Neukum <oneukum@suse.com>
Cc: linux-usb@vger.kernel.org
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20230322195515.1267197-81-bvanassche@acm.org
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>