clean up unused variable warnings

Change-Id: I9467d7a50eac32d8e8f3a2f26db818e47c93c94b
diff --git a/vp8/vp8_dx_iface.c b/vp8/vp8_dx_iface.c
index 99657e0..cca17c2 100644
--- a/vp8/vp8_dx_iface.c
+++ b/vp8/vp8_dx_iface.c
@@ -618,8 +618,8 @@
                                         int ctr_id,
                                         va_list args)
 {
-    vp8_postproc_cfg_t *data = va_arg(args, vp8_postproc_cfg_t *);
 #if CONFIG_POSTPROC
+    vp8_postproc_cfg_t *data = va_arg(args, vp8_postproc_cfg_t *);
 
     if (data)
     {