tifm: constify the struct tifm_bus_type usage

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

Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
Link: https://lore.kernel.org/r/20240423023810.1889264-1-chentao@kylinos.cn


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>