mtd: nand: Add a helper to retrieve the number of ECC bytes per step

This operation is very common and deserves a helper. It of course only
works after the ECC engine initialization.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Tested-by: Adam Ford <aford173@gmail.com> #logicpd Torpedo
Link: https://lore.kernel.org/linux-mtd/20210127203020.9574-6-miquel.raynal@bootlin.com

include/linux/mtd/nand.h

@@ -597,6 +597,16 @@ nanddev_get_ecc_nsteps(struct nand_device *nand)
 	return nand->ecc.ctx.nsteps;
 }
 
+/**
+ * nanddev_get_ecc_bytes_per_step() - Extract the number of ECC bytes per step
+ * @nand: NAND device
+ */
+static inline unsigned int
+nanddev_get_ecc_bytes_per_step(struct nand_device *nand)
+{
+	return nand->ecc.ctx.total / nand->ecc.ctx.nsteps;
+}
+
 /**
  * nanddev_get_ecc_requirements() - Extract the ECC requirements from a NAND
  *                                  device