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

Copy and paste error in r190935..

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@191137 91177308-0d34-0410-b5e6-96231b3b80d8

tools/clang-format/clang-format-diff.py

@@ -71,7 +71,7 @@ def main():
     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)