Fix fdt access in bundle_firmware

Will sort out unit tests to catch this sort of thing.

TBR=sjg@chromium.org
BUG=chromium-os:17753
TEST=run with --bootcmd option

Change-Id: I57737e7416c0e2783426c54a6fce6ee5797d06e1
Reviewed-on: http://gerrit.chromium.org/gerrit/4685
Tested-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Vince Laviano <vlaviano@chromium.org>
diff --git a/host/lib/bundle_firmware.py b/host/lib/bundle_firmware.py
index 05efe8a..209d188 100644
--- a/host/lib/bundle_firmware.py
+++ b/host/lib/bundle_firmware.py
@@ -219,7 +219,7 @@
       bootcmd: Boot command to use, as a string (if None this this is a nop).
     """
     if bootcmd:
-      fdt.PutString('/config/bootcmd', bootcmd)
+      self.fdt.PutString('/config/bootcmd', bootcmd)
       self._out.Info('Boot command: %s' % bootcmd)
 
   def AddConfigList(self, config_list, use_int=False):