bus: mhi: host: make mhi_bus_type const

Now that the driver core can properly handle constant struct bus_type,
move the mhi_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: Kunwu Chan <chentao@kylinos.cn>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20240823031129.49010-1-kunwu.chan@linux.dev
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

drivers/bus/mhi/host/init.c

@@ -1464,7 +1464,7 @@ static int mhi_match(struct device *dev, const struct device_driver *drv)
 	return 0;
 };
 
-struct bus_type mhi_bus_type = {
+const struct bus_type mhi_bus_type = {
 	.name = "mhi",
 	.dev_name = "mhi",
 	.match = mhi_match,

drivers/bus/mhi/host/internal.h

@@ -9,7 +9,7 @@
 
 #include "../common.h"
 
-extern struct bus_type mhi_bus_type;
+extern const struct bus_type mhi_bus_type;
 
 /* Host request register */
 #define MHI_SOC_RESET_REQ_OFFSET			0xb0