staging: vme: make vme_bus_type const

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

Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ricardo B. Marliere <ricardo@marliere.net>
Link: https://lore.kernel.org/r/20240208-bus_cleanup-staging2-v1-2-cfe906133a2c@marliere.net


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