docs: cgroup: Fix stale source file paths

Update two references to files that were moved:
- kernel/cgroup.c -> kernel/cgroup/cgroup.c
- tools/cgroup/cgroup_event_listener.c ->
  samples/cgroup/cgroup_event_listener.c

Assisted-by: Claude:claude-opus-4-6
Signed-off-by: Costa Shulyupin <costa.shul@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

Author: makelinux

Documentation/admin-guide/cgroup-v1/cgroups.rst

@@ -525,7 +525,7 @@ cgroup. It may also be taken to prevent cgroups from being
 modified, but more specific locks may be more appropriate in that
 situation.
 
-See kernel/cgroup.c for more details.
+See kernel/cgroup/cgroup.c for more details.
 
 Subsystems can take/release the cgroup_mutex via the functions
 cgroup_lock()/cgroup_unlock().

Documentation/admin-guide/cgroup-v1/memcg_test.rst

@@ -321,7 +321,7 @@ Under below explanation, we assume CONFIG_SWAP=y.
 ----------------------
 
 	Memory controller implements memory thresholds using cgroups notification
-	API. You can use tools/cgroup/cgroup_event_listener.c to test it.
+	API. You can use samples/cgroup/cgroup_event_listener.c to test it.
 
 	(Shell-A) Create cgroup and run event listener::