cros_bundle_firmware: Move default directory from /u-boot to /firmware

A recent change has U-Boot files installed in a new location. This updates
cros_bundle_firmware to use this new location.

BUG=chrome-os-partner:5459
TEST=manual:
cros_write_firmware image.bin (with no other args) and see that it picks
up the fdt correctly.

Change-Id: I6f808999425860ff4679c381c39e5e5dee73b29c
Reviewed-on: http://gerrit.chromium.org/gerrit/7721
Tested-by: Doug Anderson <dianders@chromium.org>
Reviewed-by: Doug Anderson <dianders@chromium.org>
diff --git a/host/lib/bundle_firmware.py b/host/lib/bundle_firmware.py
index 706808a..73427ad 100644
--- a/host/lib/bundle_firmware.py
+++ b/host/lib/bundle_firmware.py
@@ -133,7 +133,7 @@
     """Check provided options and select defaults."""
     if not self._board:
       raise ValueError('No board defined - please define a board to use')
-    build_root = os.path.join('##', 'build', self._board, 'u-boot')
+    build_root = os.path.join('##', 'build', self._board, 'firmware')
     if not self._fdt_fname:
       self._fdt_fname = os.path.join(build_root, 'dtb', '%s.dtb' %
           re.sub('_', '-', self._board))