mtd: Fix C++ comment in include/linux/mtd/mtd.h

C++ comments look wrong in kernel tree. Fix one.
Signed-off-by: Pavel Machek <pavel@ucw.cz>
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

include/linux/mtd/mtd.h

@@ -267,7 +267,7 @@ struct mtd_info {
 	 */
 	unsigned int bitflip_threshold;
 
-	// Kernel-only stuff starts here.
+	/* Kernel-only stuff starts here. */
 	const char *name;
 	int index;