clang-tidy: Replace NULL with nullptr

Replaced all instances of NULL with nullptr to improve type safety
and clarity, as nullptr is the modern C++ standard for null pointers.

Tested: Build verified

Change-Id: If9e6c34c48821a7cf8577a2166727ce7db06fadc
Signed-off-by: Jayanth Othayoth <ojayanth@gmail.com>
diff --git a/libpldmresponder/pdr.cpp b/libpldmresponder/pdr.cpp
index 9a149f7..0d2d12a 100644
--- a/libpldmresponder/pdr.cpp
+++ b/libpldmresponder/pdr.cpp
@@ -16,8 +16,8 @@
 {
     uint8_t* pdrData = nullptr;
     uint32_t pdrSize{};
-    auto record = pldm_pdr_find_record_by_type(inRepo.getPdr(), pdrType, NULL,
-                                               &pdrData, &pdrSize);
+    auto record = pldm_pdr_find_record_by_type(inRepo.getPdr(), pdrType,
+                                               nullptr, &pdrData, &pdrSize);
     while (record)
     {
         PdrEntry pdrEntry{};