alinux: psi: using cpuacct_cgrp_id under CONFIG_CGROUP_CPUACCT

This is to fix the build error if CONFIG_CGROUP_CPUACCT is not enabled.
  kernel/sched/psi.c: In function 'iterate_groups':
  kernel/sched/psi.c:732:31: error: 'cpuacct_cgrp_id' undeclared (first use in this function); did you mean 'cpuacct_charge'?
Reported-by: Nkbuild test robot <lkp@intel.com>
Fixes: 1f49a738 ("alinux: psi: Support PSI under cgroup v1")
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Reviewed-by: NXunlei Pang <xlpang@linux.alibaba.com>

kernel/sched/psi.c

@@ -729,7 +729,11 @@ static struct psi_group *iterate_groups(struct task_struct *task, void **iter)
 		if (static_branch_likely(&psi_v1_disabled))
 			cgroup = task->cgroups->dfl_cgrp;
 		else
+#ifdef CONFIG_CGROUP_CPUACCT
 			cgroup = task_cgroup(task, cpuacct_cgrp_id);
+#else
+			cgroup = NULL;
+#endif
 	} else if (*iter == &psi_system)
 		return NULL;
 	else