Modernize codebase by replacing NULL with nullptr

Fixes -Wzero-as-null-pointer-constant warning for binder.

Test: m
Bug: 68236239
Change-Id: I8184bd6aa4ebff1bd8c88dad16886e98df853b03
diff --git a/libutils/include/utils/StrongPointer.h b/libutils/include/utils/StrongPointer.h
index 9cd278f1..360fce5 100644
--- a/libutils/include/utils/StrongPointer.h
+++ b/libutils/include/utils/StrongPointer.h
@@ -52,7 +52,7 @@
 template<typename T>
 class sp {
 public:
-    inline sp() : m_ptr(0) { }
+    inline sp() : m_ptr(nullptr) { }
 
     sp(T* other);  // NOLINT(implicit)
     sp(const sp<T>& other);
@@ -230,7 +230,7 @@
 void sp<T>::clear() {
     if (m_ptr) {
         m_ptr->decStrong(this);
-        m_ptr = 0;
+        m_ptr = nullptr;
     }
 }