bundle: Default device tree filename to *.dtb

We have switched to compiled device trees in the /build/<board>/firmware
directory quite a while ago, and ever since cros_write_firmware has been
broken without and explicit -d argument. Let's just fix this.

(Also restricts the name auto-detection to just use prefixes, since
otherwise our ...-revX.dtb files would confuse it.)

BUG=None
TEST=cros_write_firmware -i <valid image> -b peach_pit just works.

Change-Id: I9d855fdb55290c726cb8b35dbe6378c65991689b
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/65389
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/host/lib/bundle_firmware.py b/host/lib/bundle_firmware.py
index aedfe17..dfcc06b 100644
--- a/host/lib/bundle_firmware.py
+++ b/host/lib/bundle_firmware.py
@@ -357,24 +357,24 @@
       Selected FDT filename, after validation.
     """
     build_root = self._GetBuildRoot()
-    dir_name = os.path.join(build_root, 'dts')
+    dir_name = os.path.join(build_root, 'dtb')
     if not fname:
       # Figure out where the file should be, and the name we expect.
       base_name = re.sub('_', '-', self._board)
 
       # In case the name exists with a prefix or suffix, find it.
-      wildcard = os.path.join(dir_name, '*%s*.dts' % base_name)
+      wildcard = os.path.join(dir_name, '*%s.dtb' % base_name)
       found_list = glob.glob(self._tools.Filename(wildcard))
       if len(found_list) == 1:
         fname = found_list[0]
       else:
         # We didn't find anything definite, so set up our expected name.
-        fname = os.path.join(dir_name, '%s.dts' % base_name)
+        fname = os.path.join(dir_name, '%s.dtb' % base_name)
 
     # Convert things like 'exynos5250-daisy' into a full path.
     root, ext = os.path.splitext(fname)
     if not ext and not os.path.dirname(root):
-      fname = os.path.join(dir_name, '%s.dts' % root)
+      fname = os.path.join(dir_name, '%s.dtb' % root)
     return fname
 
   def CheckOptions(self):