UBI: introduce helpers dbg_chk_{io, gen}

With this patch code is a bit more readable and there's no
generated code or functionality impact.
Furthermore, this abstracts implementation details and
will allow to change ubi_debug_info in a less invasive way.

Signed-off-by: Ezequiel Garcia <elezegarcia@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

drivers/mtd/ubi/vmt.c

@@ -847,7 +847,7 @@ static int self_check_volumes(struct ubi_device *ubi)
 {
 	int i, err = 0;
 
-	if (!ubi->dbg->chk_gen)
+	if (!ubi_dbg_chk_gen(ubi))
 		return 0;
 
 	for (i = 0; i < ubi->vtbl_slots; i++) {