[MTD] [NAND] AT91 hardware ECC compile fix for at91sam9263 / at91sam9260

The sam926x docs allegedly don't list an "ECC_PARITY" field, and the 
header files in the upstream kernel don't have it either.

Masking with it was useless anyway, so just remove it.

Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>