sh: intc: Make intc_subsys const

sh: intc: Make intc_subsys const

Now that the driver core can properly handle constant struct bus_type,
move the make intc_subsys variable to be a constant structure as well,
placing it into read-only memory which can not be modified at runtime.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ricardo B. Marliere <ricardo@marliere.net>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Link: https://lore.kernel.org/r/20240208-bus_cleanup-sh2-v1-1-729277400893@marliere.net
Signed-off-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>