mtd: Drop superfluous const qualifier

The compiler will ignore it anyway:

  include/linux/mtd/mtd.h:342:15: warning: type qualifiers ignored on function return type [-Wignored-qualifiers]

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
index 6751fb5..3ffcd40 100644
--- a/include/linux/mtd/mtd.h
+++ b/include/linux/mtd/mtd.h
@@ -339,7 +339,7 @@
 	dev_set_ofnode(mtd->dev, node);
 }
 
-static inline const ofnode mtd_get_ofnode(struct mtd_info *mtd)
+static inline ofnode mtd_get_ofnode(struct mtd_info *mtd)
 {
 	return dev_ofnode(mtd->dev);
 }