mtd: nand: mtk-ecc: stop on ECC idle timeouts

mtd: nand: mtk-ecc: stop on ECC idle timeouts

mtk_ecc_wait_idle() logs when the encoder or decoder does not become
idle, but returns void. Callers can therefore configure a non-idle ECC
engine or read parity bytes after an unconfirmed encoder idle state.

Return the idle poll result and propagate it from the enable and encode
paths that require the engine to be idle before continuing.

Fixes: 1d6b1e464950 ("mtd: mediatek: driver for MTK Smart Device")
Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>