fs: Fix syntax issues in comments

hulk inclusion
category: cleanup
bugzilla: https://gitee.com/openeuler/kernel/issues/I8HWD1



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There are syntax errors in the comments of the code section that detects
opening write opened block devices exclusively and opening an exclusive
opened block device for write, which need to be fixed.

Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com>