clang-format is in a separate package now

Change-Id: I77b45d3a4fd7ad8c7a50b090c706df6d8fc72abf
diff --git a/aos/build/build.py b/aos/build/build.py
index 77edd89..e948eb4 100755
--- a/aos/build/build.py
+++ b/aos/build/build.py
@@ -726,8 +726,8 @@
   def check_installed(self, platforms, is_deploy):
     packages = set(('lzip', 'm4', 'realpath'))
     packages.add('ruby')
-    # clang-format from here gets used for all versions.
     packages.add('clang-3.5')
+    packages.add('clang-format-3.5')
     packages.add('arm-eabi-gcc')
     for platform in platforms:
       if platform.architecture() == 'arm':