trivial: fix where cgroup documentation is not correctly referred to

cgroup documentation was moved to Documentation/cgroups/. There are some
places that still refer to Documentation/controllers/,
Documentation/cgroups.txt and Documentation/cpusets.txt. Fix those.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Paul Menage <menage@google.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/Documentation/scheduler/sched-rt-group.txt b/Documentation/scheduler/sched-rt-group.txt
index 3ef339f..5ba4d3f 100644
--- a/Documentation/scheduler/sched-rt-group.txt
+++ b/Documentation/scheduler/sched-rt-group.txt
@@ -126,7 +126,7 @@
 to control the CPU time reserved for each control group instead.
 
 For more information on working with control groups, you should read
-Documentation/cgroups.txt as well.
+Documentation/cgroups/cgroups.txt as well.
 
 Group settings are checked against the following limits in order to keep the configuration
 schedulable: