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 <[e-mail]>
Signed-off-by: Boris Brezillon <[e-mail]>

drivers/mtd/mtdcore.c

···
 };
 ATTRIBUTE_GROUPS(mtd);
 
-static struct device_type mtd_devtype = {
+static const struct device_type mtd_devtype = {
 	.name		= "mtd",
 	.groups		= mtd_groups,
 	.release	= mtd_release,