eulerfs: fix null-ptr-dereference when allocate page failed

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I78RYS


CVE: NA

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Currently, the caller of eufs_alloc_page() and eufs_zalloc_page() expect
that allocation won't fail, otherwise null_ptr_dereference will be
triggered.

Fix this problem by adding flag __GFP_NOFAIL.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>