dt-bindings: mtd: ingenic: Change 'BCH' to 'ECC' in documentation

The JZ4740 ECC hardware is not BCH but Reed-Solomon, so it makes more
sense to use the more generic ECC term.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>