Fix compilation warning introduced in r327654

The compiler complained about

../tools/clang/lib/CodeGen/CGOpenMPRuntimeNVPTX.cpp:184:15: error: unused variable 'CSI' [-Werror,-Wunused-variable]
    if (auto *CSI = CGF.CapturedStmtInfo) {
              ^
1 error generated.

I don't know this code but it seems like an easy fix so I push it anyway
to get rid of the warning.

llvm-svn: 327694