clang-tidy: Change NULL to nullptr

Change-Id: I3b33aca08785ceb90c15c5155c9bb13b04e95d4e
Signed-off-by: Matt Spinler <spinler@us.ibm.com>
diff --git a/extensions/openpower-pels/fapi_data_process.cpp b/extensions/openpower-pels/fapi_data_process.cpp
index a7cd1b4..d57c9da 100644
--- a/extensions/openpower-pels/fapi_data_process.cpp
+++ b/extensions/openpower-pels/fapi_data_process.cpp
@@ -159,7 +159,7 @@
     std::memcpy(&targetInfo.physBinPath, physBinPath.data(),
                 sizeof(targetInfo.physBinPath));
 
-    int ret = pdbg_target_traverse(NULL, pdbgCallbackToGetTgtReqAttrsVal,
+    int ret = pdbg_target_traverse(nullptr, pdbgCallbackToGetTgtReqAttrsVal,
                                    &targetInfo);
     if (ret == 0)
     {