Documentation: dt: mtd: drop "soft_bch" from example

Commit 32698aafc9 (Documentation: devicetree: deprecate "soft_bch"
nand-ecc-mode value, 2016-04-22) deprecated "soft_bch". Update the example to
match.

Signed-off-by: Baruch Siach <[email protected]>
Acked-by: Rafał Miłecki <[email protected]>
Acked-by: Rob Herring <[email protected]>
Acked-by: Boris Brezillon <[email protected]>
Signed-off-by: Brian Norris <[email protected]>

Documentation/devicetree/bindings/mtd/nand.txt

@@ -53,7 +53,8 @@ Example:
 
 		nand@0 {
 			reg = <0>;
-			nand-ecc-mode = "soft_bch";
+			nand-ecc-mode = "soft";
+			nand-ecc-algo = "bch";
 
 			/* controller specific properties */
 		};