Fix a potential problem with header file references.

Change-Id: Ibdcb83a76827f49df2703023851dcd163a3cb008
diff --git a/av1/encoder/tpl_model.h b/av1/encoder/tpl_model.h
index 18af405..cbbf11e 100644
--- a/av1/encoder/tpl_model.h
+++ b/av1/encoder/tpl_model.h
@@ -20,6 +20,8 @@
 struct EncodeFrameParams;
 struct EncodeFrameInput;
 
+#include "av1/encoder/encoder.h"
+
 static INLINE BLOCK_SIZE convert_length_to_bsize(int length) {
   switch (length) {
     case 64: return BLOCK_64X64;