codec2: Fix comment about B_FRAME.

B_FRAME is bidirectionally predicted frame, either forward or backward or together of them thru blending.

Change-Id: Ie7aebe00fcb929cb00abe0fd25b32ec625cbb0f0
diff --git a/media/codec2/core/include/C2Config.h b/media/codec2/core/include/C2Config.h
index 2cc7ab7..feaa98c 100644
--- a/media/codec2/core/include/C2Config.h
+++ b/media/codec2/core/include/C2Config.h
@@ -1673,7 +1673,7 @@
     SYNC_FRAME = (1 << 0),  ///< sync frame, e.g. IDR
     I_FRAME    = (1 << 1),  ///< intra frame that is completely encoded
     P_FRAME    = (1 << 2),  ///< inter predicted frame from previous frames
-    B_FRAME    = (1 << 3),  ///< backward predicted (out-of-order) frame
+    B_FRAME    = (1 << 3),  ///< bidirectional predicted (out-of-order) frame
 )
 
 /**