mtg: docg3: use free_bch() instead of kfree()

Use free_bch() instead of kfree() to free init_bch()
allocated data.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/devices/docg3.c

@@ -2097,7 +2097,7 @@ notfound:
 	ret = -ENODEV;
 	dev_info(dev, "No supported DiskOnChip found\n");
 err_probe:
-	kfree(cascade->bch);
+	free_bch(cascade->bch);
 	for (floor = 0; floor < DOC_MAX_NBFLOORS; floor++)
 		if (cascade->floors[floor])
 			doc_release_device(cascade->floors[floor]);