The usba_gadget_template structure is only copied into another
structure, so make it const.

The opportunity for this change was found using Coccinelle.
Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>
Acked-by: Cristian Birsan <cristian.birsan@microchip.com>
Link: https://lore.kernel.org/r/1577864614-5543-5-git-send-email-Julia.Lawall@inria.frSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>