Declare the src parameter as pointer to const

Change-Id: I9d4eda5d8efddf4fc523871c9bec92216babdc7d
diff --git a/av1/encoder/lookahead.c b/av1/encoder/lookahead.c
index 0f7c819..f2bcb27 100644
--- a/av1/encoder/lookahead.c
+++ b/av1/encoder/lookahead.c
@@ -84,7 +84,7 @@
   return NULL;
 }
 
-int av1_lookahead_push(struct lookahead_ctx *ctx, YV12_BUFFER_CONFIG *src,
+int av1_lookahead_push(struct lookahead_ctx *ctx, const YV12_BUFFER_CONFIG *src,
                        int64_t ts_start, int64_t ts_end, int use_highbitdepth,
                        aom_enc_frame_flags_t flags) {
   struct lookahead_entry *buf;
diff --git a/av1/encoder/lookahead.h b/av1/encoder/lookahead.h
index 9569b96..8861fd1 100644
--- a/av1/encoder/lookahead.h
+++ b/av1/encoder/lookahead.h
@@ -84,7 +84,7 @@
  * \param[in] use_highbitdepth Tell if HBD is used
  * \param[in] flags       Flags set on this frame
  */
-int av1_lookahead_push(struct lookahead_ctx *ctx, YV12_BUFFER_CONFIG *src,
+int av1_lookahead_push(struct lookahead_ctx *ctx, const YV12_BUFFER_CONFIG *src,
                        int64_t ts_start, int64_t ts_end, int use_highbitdepth,
                        aom_enc_frame_flags_t flags);