sched, cgroups: Fix module export

I have exported it in d11c563d - but cgroups.c did not have module.h included ...

Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <1266887105-1528-6-git-send-email-paulmck@linux.vnet.ibm.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

kernel/cgroup.c

@@ -23,6 +23,7 @@
  */
 
 #include <linux/cgroup.h>
+#include <linux/module.h>
 #include <linux/ctype.h>
 #include <linux/errno.h>
 #include <linux/fs.h>