[NVPTX] Clean up nested !strconcat calls.

!strconcat is a variadic function; it will concatenate an arbitrary
number of strings.  There's no need to nest it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@292305 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed