aom_free_frame_buffer should return 0 on success.

This bug was introduced in commit
02affebbe5c16882eab0ddcdc53dafcee911a1c3.

Change-Id: I0f965584c04a6db69b175aaec49edbeced26bc59
diff --git a/aom_scale/generic/yv12config.c b/aom_scale/generic/yv12config.c
index 493663e..08b82b2 100644
--- a/aom_scale/generic/yv12config.c
+++ b/aom_scale/generic/yv12config.c
@@ -38,6 +38,7 @@
       u_buffer and v_buffer point to buffer_alloc and are used.  Clear out
       all of this so that a freed pointer isn't inadvertently used */
     memset(ybf, 0, sizeof(YV12_BUFFER_CONFIG));
+    return 0;
   }
 
   return AOM_CODEC_MEM_ERROR;