[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/daemon/framebuffer_service.cpp b/daemon/framebuffer_service.cpp
index 6c3a225..20e03f9 100644
--- a/daemon/framebuffer_service.cpp
+++ b/daemon/framebuffer_service.cpp
@@ -75,7 +75,7 @@
         adb_close(fds[0]);
         adb_close(fds[1]);
         const char* command = "screencap";
-        const char *args[2] = {command, NULL};
+        const char *args[2] = {command, nullptr};
         execvp(command, (char**)args);
         exit(1);
     }
@@ -182,7 +182,7 @@
 done:
     adb_close(fds[0]);
 
-    TEMP_FAILURE_RETRY(waitpid(pid, NULL, 0));
+    TEMP_FAILURE_RETRY(waitpid(pid, nullptr, 0));
 pipefail:
     adb_close(fd);
 }