Fix typo in aomenc when using the key & val API.

Change-Id: I146806d485301eb227f1c061983dc056957bd884
(cherry picked from commit 0b822bed92b9e3ebcdd4d2fddba594be8aa02e60)

apps/aomenc.c

diff --git a/apps/aomenc.c b/apps/aomenc.c
index 5eb8c82..b86b80a 100644
--- a/apps/aomenc.c
+++ b/apps/aomenc.c
@@ -853,9 +853,9 @@
   }
 
   /* Point either to the next free element or the first instance of this
-   * control.
+   * option.
    */
-  for (j = 0; j < config->arg_ctrl_cnt; j++)
+  for (j = 0; j < config->arg_key_val_cnt; j++)
     if (strcmp(name, config->arg_key_vals[j][0]) == 0) break;
 
   /* Update/insert */