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>
diff --git a/drivers/mtd/ubi/vtbl.c b/drivers/mtd/ubi/vtbl.c
index 926e3df..d77b1c1 100644
--- a/drivers/mtd/ubi/vtbl.c
+++ b/drivers/mtd/ubi/vtbl.c
@@ -858,7 +858,7 @@
  */
 static void self_vtbl_check(const struct ubi_device *ubi)
 {
-	if (!ubi->dbg->chk_gen)
+	if (!ubi_dbg_chk_gen(ubi))
 		return;
 
 	if (vtbl_check(ubi, ubi->vtbl)) {