mfd: mcp-core: Make mcp_bus_type const

Now that the driver core can properly handle constant struct bus_type,
move the mcp_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 <[e-mail]>
Signed-off-by: "Ricardo B. Marliere" <[e-mail]>
Reviewed-by: Greg Kroah-Hartman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

drivers/mfd/mcp-core.c

···
 	drv->remove(mcp);
 }
 
-static struct bus_type mcp_bus_type = {
+static const struct bus_type mcp_bus_type = {
 	.name		= "mcp",
 	.match		= mcp_bus_match,
 	.probe		= mcp_bus_probe,