cgpt: add back format field

Previous commit here accidentally deleted the format field.

BUG=chromium:329112,chromium:339298
TEST=building for sonic doesn't warn anymore

Change-Id: If9fded31ac938d1ee1b9fcb8cd5457ff0bec82b4
Reviewed-on: https://chromium-review.googlesource.com/184302
Reviewed-by: Gaurav Shah <gauravsh@chromium.org>
Reviewed-by: Chris Sosa <sosa@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/build_library/cgpt.py b/build_library/cgpt.py
index 52bdc4e..f24f6b8 100755
--- a/build_library/cgpt.py
+++ b/build_library/cgpt.py
@@ -194,7 +194,7 @@
   valid_keys = set(('_comment', 'hybrid_mbr', 'metadata', 'layouts', 'parent'))
   valid_layout_keys = set((
       '_comment', 'num', 'blocks', 'block_size', 'fs_blocks', 'fs_block_size',
-      'uuid', 'label', 'fs_format', 'type', 'features', 'num'))
+      'uuid', 'label', 'format', 'fs_format', 'type', 'features', 'num'))
 
   config = _LoadStackedPartitionConfig(filename)