mtd: spinand: micron: correct bitmask for ecc status

Valid bitmask is 0x70 in the status register.

Fixes: a508e887 ("mtd: spinand: Add initial support for Micron MT29F2G01ABAGD")
Signed-off-by: Martin Kurbanov <mmkurbanov@sberdevices.ru>
Reviewed-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20230905145637.139068-1-mmkurbanov@sberdevices.ru