fromupstream: fix pylint error: Redefining built-in 'file'

Apparently the commit bdbb9cc2c9dc ("fromupstream: Tag commits with
BACKPORT if appropriate") was submitted without running (or with
ignoring) the pre-upload hooks.  Thus it wasn't pyling clean.  After
that patch, we get this warning:

  W: 29, 8: Redefining built-in 'file' (redefined-builtin)

Let's fix it.

BUG=None
TEST=No more pylint errors

Change-Id: Iee6ececc7ac459b91d6a9328c80ad0d1e9195bcf
Reviewed-on: https://chromium-review.googlesource.com/1035455
Commit-Ready: Douglas Anderson <dianders@chromium.org>
Tested-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
diff --git a/contrib/fromupstream.py b/contrib/fromupstream.py
index 5818f05..f61d9ed 100755
--- a/contrib/fromupstream.py
+++ b/contrib/fromupstream.py
@@ -24,12 +24,12 @@
     """Report conflicting files."""
     resolutions = ('DD', 'AU', 'UD', 'UA', 'DU', 'AA', 'UU')
     conflicts = []
-    files = subprocess.check_output(['git', 'status', '--porcelain',
+    lines = subprocess.check_output(['git', 'status', '--porcelain',
                                      '--untracked-files=no']).split('\n')
-    for file in files:
-        if not file:
+    for line in lines:
+        if not line:
             continue
-        resolution, name = file.split(None, 1)
+        resolution, name = line.split(None, 1)
         if resolution in resolutions:
             conflicts.append('   ' + name)
     if not conflicts: