mm/sharepool: delete unnecessary judgment

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5PIA2
CVE: NA

--------------------------------

When a process is added to a group, mm->mm_users increases by one.
When a process is deleted from a group, mm->mm_users decreases by
one. It is not possible to reduce to 0 because this function is
preceded by get_task_mm.
Signed-off-by: NZhou Guanghui <zhouguanghui1@huawei.com>

mm/share_pool.c

@@ -1621,11 +1621,7 @@ int mg_sp_group_del_task(int pid, int spg_id)
 	list_del(&spg_node->group_node);
 	mm->sp_group_master->count--;
 	kfree(spg_node);
-	if (atomic_sub_and_test(1, &mm->mm_users)) {
-		up_write(&sp_group_sem);
-		WARN(1, "Invalid user counting\n");
-		return -EINVAL;
-	}
+	atomic_dec(&mm->mm_users);
 
 	up_write(&sp_group_sem);