ARM: dts: AM33xx: updated default ECC scheme in nand-ecc-opt

This patch updated MTD/NAND DT node binding to replace deprecated bindings
as per following commit.
    commit ac65caf5
    ARM: OMAP2+: cleaned-up DT support of various ECC schemes
    Also Refer: Documentation/devicetree/bindings/mtd/gpmc-nand.txt

Reviewed-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Pekon Gupta <pekon@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>