mtd: nand: omap_gpmc: Fix NAND in SPL for AM335x

AM335x uses a special driver "am335x_spl_bch.c" as SPL
NAND loader. This driver expects 1 sector at a time ECC
and doesn't work well with multi-sector ECC that was implemented in
commit 04fcd258 ("mtd: rawnand: omap_gpmc: Fix BCH6/16 HW based correction")

Additionally, the omap_elm driver does not support multi sector ECC and will
need more work and tests to get multi sector working correctly on all
platforms.

Switch back to 1 sector at a time read/ECC.

Fixes: 04fcd258 ("mtd: rawnand: omap_gpmc: Fix BCH6/16 HW based correction")
Signed-off-by: Roger Quadros <rogerq@kernel.org>
Tested-by: Enrico Leto <enrico.leto@siemens.com>
Tested-by: Heiko Schocher <hs@denx.de>
Link: https://lore.kernel.org/all/20231211114600.4414-2-rogerq@kernel.org/


Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>