gralloc: Update implementation defined format in buffer info

Change-Id: I1a53c5524587b9d5fe318b63152169a77f11a0b5
diff --git a/gralloc/gr_buf_mgr.cpp b/gralloc/gr_buf_mgr.cpp
index 2e9d597..70fb483 100644
--- a/gralloc/gr_buf_mgr.cpp
+++ b/gralloc/gr_buf_mgr.cpp
@@ -324,6 +324,7 @@
 
   int buffer_type = GetBufferType(format);
   BufferInfo info = GetBufferInfo(descriptor);
+  info.format = format;
   GetBufferSizeAndDimensions(info, &size, &alignedw, &alignedh);
   size = (bufferSize >= size) ? bufferSize : size;