[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/daemon/auth.cpp b/adb/daemon/auth.cpp
index f0c3629..180df8f 100644
--- a/adb/daemon/auth.cpp
+++ b/adb/daemon/auth.cpp
@@ -100,7 +100,7 @@
 
 static void usb_disconnected(void* unused, atransport* t) {
     LOG(INFO) << "USB disconnect";
-    usb_transport = NULL;
+    usb_transport = nullptr;
     needs_retry = false;
 }
 
@@ -200,7 +200,7 @@
         return;
     }
 
-    listener_fde = fdevent_create(fd, adbd_auth_listener, NULL);
+    listener_fde = fdevent_create(fd, adbd_auth_listener, nullptr);
     fdevent_add(listener_fde, FDE_READ);
 }