ipack: make ipack_bus_type const

Now that the driver core can properly handle constant struct bus_type,
move the ipack_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>
Acked-by: Vaibhav Gupta <vaibhavgupta40@gmail.com>
Link: https://lore.kernel.org/r/20240204-bus_cleanup-ipack-v1-1-aef5e8f84d01@marliere.net


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