mtd: rawnand: Annotate implicit fall through in nand_scan_tail

There is a plan to build the kernel with -Wimplicit-fallthrough and
these places in the code produced warnings (W=1).

This commit removes the following warnings:

  drivers/mtd/nand/raw/nand_base.c:5556:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
  drivers/mtd/nand/raw/nand_base.c:5575:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
  drivers/mtd/nand/raw/nand_base.c:5613:13: warning: this statement may fall through [-Wimplicit-fallthrough=]
Signed-off-by: Mathieu Malaterre <malat@debian.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

drivers/mtd/nand/raw/nand_base.c

@@ -5537,6 +5537,7 @@ static int nand_scan_tail(struct nand_chip *chip)
 		}
 		if (!ecc->read_page)
 			ecc->read_page = nand_read_page_hwecc_oob_first;
+		/* fall through */
 
 	case NAND_ECC_HW:
 		/* Use standard hwecc read page function? */
@@ -5556,6 +5557,7 @@ static int nand_scan_tail(struct nand_chip *chip)
 			ecc->read_subpage = nand_read_subpage;
 		if (!ecc->write_subpage && ecc->hwctl && ecc->calculate)
 			ecc->write_subpage = nand_write_subpage_hwecc;
+		/* fall through */
 
 	case NAND_ECC_HW_SYNDROME:
 		if ((!ecc->calculate || !ecc->correct || !ecc->hwctl) &&
@@ -5593,6 +5595,7 @@ static int nand_scan_tail(struct nand_chip *chip)
 			ecc->size, mtd->writesize);
 		ecc->mode = NAND_ECC_SOFT;
 		ecc->algo = NAND_ECC_HAMMING;
+		/* fall through */
 
 	case NAND_ECC_SOFT:
 		ret = nand_set_ecc_soft_ops(chip);