mtg: docg3: potential divide by zero in doc_write_oob()

If we set oobdelta to zero then we will either return -EINVAL or hit
a divide (modulus) by zero on the next line when we check
"(ooblen % oobdelta)".  It's better to just return -EINVAL here instead.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
diff --git a/drivers/mtd/devices/docg3.c b/drivers/mtd/devices/docg3.c
index d34d83b..8510ccb 100644
--- a/drivers/mtd/devices/docg3.c
+++ b/drivers/mtd/devices/docg3.c
@@ -1440,7 +1440,7 @@
 		oobdelta = mtd->ecclayout->oobavail;
 		break;
 	default:
-		oobdelta = 0;
+		return -EINVAL;
 	}
 	if ((len % DOC_LAYOUT_PAGE_SIZE) || (ooblen % oobdelta) ||
 	    (ofs % DOC_LAYOUT_PAGE_SIZE))