mtd: make device_type const

Make this const as it is only stored in the type field of a device
structure, which is const.
Done using Coccinelle.
Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>

drivers/mtd/mtdcore.c

@@ -340,7 +340,7 @@ static struct attribute *mtd_attrs[] = {
 };
 ATTRIBUTE_GROUPS(mtd);
 
-static struct device_type mtd_devtype = {
+static const struct device_type mtd_devtype = {
 	.name		= "mtd",
 	.groups		= mtd_groups,
 	.release	= mtd_release,