cgroup: kill unused variable

Signed-off-by: Jeff Garzik <[e-mail]>

kernel/cgroup.c

···
 static int proc_cgroupstats_show(struct seq_file *m, void *v)
 {
 	int i;
-	struct cgroupfs_root *root;
 
 	seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\n");
 	mutex_lock(&cgroup_mutex);