staging: gasket: apex: Make structure apex_desc constant

staging: gasket: apex: Make structure apex_desc constant

Static structure apex_desc, of type gasket_driver_desc, is used only as
an argument to the functions gasket_register_device() and
gasket_unregister_device(). In the definitions of both these functions,
their parameter is declared as const. Hence make apex_desc itself
constant to protect it from modification.
Issue found with Coccinelle.

Signed-off-by: Nishka Dasgupta <nishkadg.linux@gmail.com>
Link: https://lore.kernel.org/r/20190815054924.643-1-nishkadg.linux@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>