mtd: nand: Add a new helper to retrieve the ECC context

Introduce nand_to_ecc_ctx() which will allow to easily jump to the
private pointer of an ECC context given a NAND device. This is very
handy, from the prepare or finish ECC hook, to get the internal context
out of the NAND device object.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20211216111654.238086-14-miquel.raynal@bootlin.com

include/linux/mtd/nand.h

@@ -990,6 +990,11 @@ int nanddev_markbad(struct nand_device *nand, const struct nand_pos *pos);
 int nanddev_ecc_engine_init(struct nand_device *nand);
 void nanddev_ecc_engine_cleanup(struct nand_device *nand);
 
+static inline void *nand_to_ecc_ctx(struct nand_device *nand)
+{
+	return nand->ecc.ctx.priv;
+}
+
 /* BBT related functions */
 enum nand_bbt_block_status {
 	NAND_BBT_BLOCK_STATUS_UNKNOWN,