mtd: rawnand: jz4780: annotate implicit fall throughs

There is a plan to build the kernel with -Wimplicit-fallthrough and
these places in the code produced warnings. Fix them up.
Signed-off-by: Mathieu Malaterre <malat@debian.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

drivers/mtd/nand/raw/jz4780_bch.c

@@ -136,8 +136,10 @@ static void jz4780_bch_read_parity(struct jz4780_bch *bch, void *buf,
 	switch (size8) {
 	case 3:
 		dest8[2] = (val >> 16) & 0xff;
+		/* fall through */
 	case 2:
 		dest8[1] = (val >> 8) & 0xff;
+		/* fall through */
 	case 1:
 		dest8[0] = val & 0xff;
 		break;