cdx: make cdx_bus_type constant

cdx: make cdx_bus_type constant

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

Cc: Nipun Gupta <nipun.gupta@amd.com>
Cc: Nikhil Agarwal <nikhil.agarwal@amd.com>
Acked-by: Nipun Gupta <nipun.gupta@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://patch.msgid.link/2025091439-sustained-acorn-4af4@gregkh
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>