f2fs: fix to cover read extent cache access with lock

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                    "product": "Linux",
                    "vendor": "Linux",
                    "defaultStatus": "affected",
                    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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                        "fs/f2fs/extent_cache.c",
                        "fs/f2fs/f2fs.h",
                        "fs/f2fs/inode.c"
                    ],
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