mmc: core: make mmc_bus_type const

Now that the driver core can properly handle constant struct bus_type,
move the mmc_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>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20240203-bus_cleanup-mmc-v1-2-ad054dce8dc3@marliere.netSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/core/bus.c

@@ -214,7 +214,7 @@ static const struct dev_pm_ops mmc_bus_pm_ops = {
 	SET_SYSTEM_SLEEP_PM_OPS(mmc_bus_suspend, mmc_bus_resume)
 };
 
-static struct bus_type mmc_bus_type = {
+static const struct bus_type mmc_bus_type = {
 	.name		= "mmc",
 	.dev_groups	= mmc_dev_groups,
 	.uevent		= mmc_bus_uevent,