Fix incorrect use of Path.getRoot()

Author: jbachorik

dd-java-agent/agent-profiling/profiling-controller/src/main/java/com/datadog/profiling/controller/TempLocationManager.java

@@ -465,7 +465,7 @@ private void createTempDir(Path tempDir) {
       // we will find the first offender not having the expected permissions and fail the check
       if (isPosixFs) {
         // take the first subfolder below the base temp dir
-        Path root = baseTempDir.resolve(baseTempDir.relativize(tempDir).getRoot());
+        Path root = baseTempDir.resolve(baseTempDir.relativize(tempDir).getName(0));
         try {
           AtomicReference<Path> failed = new AtomicReference<>();
           Files.walkFileTree(