mtd: nand: omap: fix HAM1_SW ecc using default value for ecc.size

Commit "mtd: nand: omap: enable BCH ECC scheme using ELM for generic
platform" (d016dc42) changed the way
software ECC is configured, both during boot, and during ecc switch, in a way
that is not backwards compatible with older systems:

Older version of omap_gpmc.c always assigned ecc.size = 0 when configuring
for software ecc, relying on nand_scan_tail() to select a default for ecc.size
(256), while the new version of omap_gpmc.c assigns ecc.size = pagesize,
which is likely to not be 256.

Since 1 bit hamming sw ecc is only meant to be used by legacy devices, revert
to the original behavior.

Cc: Igor Grinberg <grinberg@compulab.co.il>
Cc: Tom Rini <trini@ti.com>
Cc: Scott Wood <scottwood@freescale.com>
Cc: Pekon Gupta <pekon@ti.com>
Signed-off-by: Nikita Kiryanov <nikita@compulab.co.il>
Acked-by: Pekon Gupta <pekon@ti.com>