dax: constify the struct device_type usage

Since commit aed65af ("drivers: make device_type const"), the driver
core can properly handle constant struct device_type. Move the
dax_mapping_type variable to be a constant structure as well, placing it
into read-only memory which can not be modified at runtime.

Cc: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Ricardo B. Marliere <[email protected]>
Reviewed-by: Dave Jiang <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Ira Weiny <[email protected]>

Author: rbmarliere

drivers/dax/bus.c

@@ -818,7 +818,7 @@ static const struct attribute_group *dax_mapping_attribute_groups[] = {
 	NULL,
 };
 
-static struct device_type dax_mapping_type = {
+static const struct device_type dax_mapping_type = {
 	.release = dax_mapping_release,
 	.groups = dax_mapping_attribute_groups,
 };