tools: dtoc: Open all binary files in binary mode

Fix an open() statement to use binary mode, so that it works as expected
with Python 3.

Signed-off-by: Simon Glass <sjg@chromium.org>

tools/dtoc/fdt.py

@@ -469,7 +469,7 @@ class Fdt:
         if self._fname:
             self._fname = fdt_util.EnsureCompiled(self._fname)
 
-            with open(self._fname) as fd:
+            with open(self._fname, 'rb') as fd:
                 self._fdt_obj = libfdt.Fdt(fd.read())
 
     @staticmethod