quota: factor out dquot_write_dquot()

maillist inclusion
category: bugfix
bugzilla: 188812,https://gitee.com/openeuler/kernel/issues/I7E0YR

Reference: https://www.spinics.net/lists/kernel/msg4844759.html



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Refactor out dquot_write_dquot() to reduce duplicate code.

Signed-off-by: Baokun Li <libaokun1@huawei.com>