[libutils]  Modernize codebase by replacing NULL with nullptr

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

Test: m
Bug: 68236239
Change-Id: I5e89ec8c42151875439d2656475a8739ab9cb7dc
diff --git a/libutils/SharedBuffer.h b/libutils/SharedBuffer.h
index 81cadff..fdf13a9 100644
--- a/libutils/SharedBuffer.h
+++ b/libutils/SharedBuffer.h
@@ -124,11 +124,11 @@
 }
 
 SharedBuffer* SharedBuffer::bufferFromData(void* data) {
-    return data ? static_cast<SharedBuffer *>(data)-1 : 0;
+    return data ? static_cast<SharedBuffer *>(data)-1 : nullptr;
 }
     
 const SharedBuffer* SharedBuffer::bufferFromData(const void* data) {
-    return data ? static_cast<const SharedBuffer *>(data)-1 : 0;
+    return data ? static_cast<const SharedBuffer *>(data)-1 : nullptr;
 }
 
 size_t SharedBuffer::sizeFromData(const void* data) {