Make gf_group->is_frame_non_ref boolean

The data type of 'is_frame_non_ref' in GF_GROUP
structure is changed from int to bool.

Change-Id: Idb7ad2689dbca90a111fbd26d234a25c6e70f3d5
diff --git a/av1/encoder/firstpass.h b/av1/encoder/firstpass.h
index 077bd85..dddab03 100644
--- a/av1/encoder/firstpass.h
+++ b/av1/encoder/firstpass.h
@@ -402,9 +402,7 @@
   // 2 : frame occurs later in encode order in a given parallel encode set.
   int frame_parallel_level[MAX_STATIC_GF_GROUP_LENGTH];
   // Indicates whether a frame should act as non-reference frame.
-  // 0 : frame is a reference frame.
-  // 1 : frame is a non-reference frame.
-  int is_frame_non_ref[MAX_STATIC_GF_GROUP_LENGTH];
+  bool is_frame_non_ref[MAX_STATIC_GF_GROUP_LENGTH];
   // Indicates whether a frame is dropped.
   bool is_frame_dropped[MAX_STATIC_GF_GROUP_LENGTH];