[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/transport.cpp b/adb/transport.cpp
index 7db9bf2..f2c40d2 100644
--- a/adb/transport.cpp
+++ b/adb/transport.cpp
@@ -404,7 +404,7 @@
 
     VLOG(TRANSPORT) << dump_packet(t->serial, "to remote", p);
 
-    if (t == NULL) {
+    if (t == nullptr) {
         fatal("Transport is null");
     }
 
@@ -467,7 +467,7 @@
 
     D("device tracker %p removed", tracker);
     if (peer) {
-        peer->peer = NULL;
+        peer->peer = nullptr;
         peer->close(peer);
     }
     device_tracker_remove(tracker);
@@ -699,7 +699,7 @@
     transport_registration_recv = s[1];
 
     transport_registration_fde =
-        fdevent_create(transport_registration_recv, transport_registration_func, 0);
+        fdevent_create(transport_registration_recv, transport_registration_func, nullptr);
     fdevent_set(transport_registration_fde, FDE_READ);
 }