[clang-tidy] Fix an unused-using-decl false positive about template arguments in

function call expression.

Summary:
The check doesn't mark the template argument as used when the template
argument is a template.

Reviewers: djasper, alexfh

Subscribers: klimek, cfe-commits

Differential Revision: https://reviews.llvm.org/D22803

llvm-svn: 277444