fs/filescontrol.c: fix warning:large integer implicitly truncated to unsigned type

hulk inclusion
category: bugfix
bugzilla: 50779
CVE: NA

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page_counter_set_max(struct page_counter *counter, unsigned long nr_pages)
the nr_pages is unsigned long, therefore change FILES_MAX to ULONG_MAX

Signed-off-by: Lu Jialin <lujialin4@huawei.com>
Reviewed-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>