quota: code cleanup for __dquot_alloc_space()

stable inclusion
from stable-v4.19.311
commit d9e4ab12b60a49204435102f8120c0d3e62583f1
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I9HJX7
CVE: CVE-2024-26878

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d9e4ab12b60a49204435102f8120c0d3e62583f1



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

[ Upstream commit df15a2a5 ]

Replace (flags & DQUOT_SPACE_RESERVE) with
variable reserve.

Signed-off-by: Chengguang Xu <cgxu519@gmx.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Stable-dep-of: 179b8c97ebf6 ("quota: Fix rcu annotations of inode dquot pointers")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Baokun Li <libaokun1@huawei.com>