mtd: nand: fix Samsung SLC detection regression

This patch fixes errors seen in identifying old Samsung SLC, due to the
following commits:

    commit e2d3a35e
    mtd: nand: detect Samsung K9GBG08U0A, K9GAG08U0F ID

    commit e3b88bd6
    mtd: nand: add generic READ ID length calculation functions

Some Samsung NAND with "5-byte" ID really appear to have 6-byte IDs, with
wraparound like:

  Samsung K9K8G08U0D
  ec d3 51 95 58 ec ec d3

  Samsung K9F1G08U0C
  ec f1 00 95 40 ec ec f1

  Samsung K9F2G08U0B
  ec da 10 95 44 00 ec da

This bad wraparound makes it hard to reliably detect the difference
between Samsung SLC with 5-byte ID and Samsung SLC with 6-byte ID.

The fix is to, for now, only use the new Samsung table for MLC. We
cannot support the new SLC (K9FAG08U0M) until Samsung gives better ID
decode information.

Note that this applies in addition to the previous regression fix:

    commit bc86cf7a
    mtd: nand: fix Samsung SLC NAND identification regression

Together, these patches completely restore the previous detection
behavior so that we cannot see any more regressions in Samsung SLC NAND
(finger crossed). With luck, I can get a hold of a Samsung
representative and stop having to cross my fingers eventually.
Reported-by: Sylwester Nawrocki <sylvester.nawrocki@gmail.com>
Tested-by: Sylwester Nawrocki <sylvester.nawrocki@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

drivers/mtd/nand/nand_base.c

@@ -2990,6 +2990,7 @@ static void nand_decode_ext_id(struct mtd_info *mtd, struct nand_chip *chip,
 	 * ID to decide what to do.
 	 */
 	if (id_len == 6 && id_data[0] == NAND_MFR_SAMSUNG &&
+			(chip->cellinfo & NAND_CI_CELLTYPE_MSK) &&
 			id_data[5] != 0x00) {
 		/* Calc pagesize */
 		mtd->writesize = 2048 << (extid & 0x03);