sama5d3: Fix Galois Field Table offsets

Offsets are described in the datasheet at section:
"11.4.4.2 NAND Flash Boot: PMECC Error Detection and Correction".

For testing I "injected" bit flips into u-boot NAND memory area,
and then read back. PMECC could not correct the errors. With the
offsets updated everything is fine.

Fixes: 3225f34e ("ARM: atmel: add sama5d3xek support")
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>