Fix clang-format-diff.py to accept -style again.

Copy and paste error in r190935..

git-svn-id: svn://svn.chromium.org/llvm-project/cfe/trunk/tools/clang-format@191137 0b72dbe1-c17f-4bc7-b9db-2b4152be0356
diff --git a/clang-format-diff.py b/clang-format-diff.py
index cb8d942..7c14178 100755
--- a/clang-format-diff.py
+++ b/clang-format-diff.py
@@ -71,7 +71,7 @@
     command = [binary, '-i', filename]
     command.extend(lines)
     if args.style:
-      command.extend(['-style', style])
+      command.extend(['-style', args.style])
     p = subprocess.Popen(command, stdout=subprocess.PIPE,
                          stderr=subprocess.PIPE,
                          stdin=subprocess.PIPE)