Fix a mutex_unlock() issue where before copy_from_user() is
not called mutex_locked.

Fixes: 4b1a29a7 ("error-injection: Support fault injection framework")
Reported-by: NHulk Robot <hulkci@huawei.com>
Signed-off-by: NLuo Meng <luomeng12@huawei.com>
Signed-off-by: NMasami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NMasami Hiramatsu <mhiramat@kernel.org>
Link: https://lore.kernel.org/bpf/160570737118.263807.8358435412898356284.stgit@devnote2