Update comment on the SCALABILITY_STRUCTURES enum

All the values of the SCALABILITY_STRUCTURES enum except SCALABILITY_SS
specify preconfigured/predefined modes. Update the comment to say 0-13.

This comment error (out of date) was introduced in
https://aomedia-review.googlesource.com/c/aom/+/57981

Note that the AV1 spec seems to specify more preconfigured modes (values
15-28), but they are not in the SCALABILITY_STRUCTURES enum.

Bug: aomedia:1838
Change-Id: Ie656033a1bc887a146acccda0a85c088a004bf3c
diff --git a/av1/common/enums.h b/av1/common/enums.h
index 1b952c4..b0644da 100644
--- a/av1/common/enums.h
+++ b/av1/common/enums.h
@@ -610,7 +610,7 @@
 } RestorationType;
 
 /*!\cond */
-// Picture prediction structures (0-12 are predefined) in scalability metadata.
+// Picture prediction structures (0-13 are predefined) in scalability metadata.
 enum {
   SCALABILITY_L1T2 = 0,
   SCALABILITY_L1T3 = 1,