vp9_svc_layercontext(): fix proto mismatch

Change-Id: I8a76d150a61662fc2e3158a49ce4e642f917029a
diff --git a/vp9/encoder/vp9_svc_layercontext.c b/vp9/encoder/vp9_svc_layercontext.c
index cd097fa..73048f8 100644
--- a/vp9/encoder/vp9_svc_layercontext.c
+++ b/vp9/encoder/vp9_svc_layercontext.c
@@ -818,7 +818,7 @@
 }
 
 // Reset on key frame: reset counters, references and buffer updates.
-void vp9_svc_reset_key_frame(VP9_COMP *cpi) {
+void vp9_svc_reset_key_frame(VP9_COMP *const cpi) {
   int sl, tl;
   SVC *const svc = &cpi->svc;
   LAYER_CONTEXT *lc = NULL;