[adb] Modernize codebase by replacing NULL with nullptr

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

Test: m
Bug: 68236239
Change-Id: Ia8c4deacafed2f3b7dbc3d4c3c77c6c632e3de81
diff --git a/adb/fdevent.cpp b/adb/fdevent.cpp
index 098a39d..dee87bd 100644
--- a/adb/fdevent.cpp
+++ b/adb/fdevent.cpp
@@ -149,7 +149,7 @@
 
 void fdevent_destroy(fdevent* fde) {
     check_main_thread();
-    if (fde == 0) return;
+    if (fde == nullptr) return;
     if (!(fde->state & FDE_CREATED)) {
         LOG(FATAL) << "destroying fde not created by fdevent_create(): " << dump_fde(fde);
     }