tools/genboardscfg.py: ignore defconfigs starting with a dot

Kconfig in U-Boot creates a temporary file configs/.tmp_defconfig
during processing "make <board>_defconfig".  The temporary file
might be left over for some reasons.

Just in case, tools/genboardscfg.py should make sure to
not read such garbage files.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/genboardscfg.py b/tools/genboardscfg.py
index f179803..31ae844 100755
--- a/tools/genboardscfg.py
+++ b/tools/genboardscfg.py
@@ -411,6 +411,8 @@
     for (dirpath, dirnames, filenames) in os.walk(CONFIG_DIR):
         dirpath = dirpath[len(CONFIG_DIR) + 1:]
         for filename in fnmatch.filter(filenames, '*_defconfig'):
+            if fnmatch.fnmatch(filename, '.*'):
+                continue
             defconfigs.append(os.path.join(dirpath, filename))
 
     # Parse all the MAINTAINERS files