[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/Timers.cpp b/libutils/Timers.cpp
index b2df9a5..c3641ef 100644
--- a/libutils/Timers.cpp
+++ b/libutils/Timers.cpp
@@ -45,7 +45,7 @@
     // is windows.
     struct timeval t;
     t.tv_sec = t.tv_usec = 0;
-    gettimeofday(&t, NULL);
+    gettimeofday(&t, nullptr);
     return nsecs_t(t.tv_sec)*1000000000LL + nsecs_t(t.tv_usec)*1000LL;
 }
 #endif