kernel/fail_function.c: remove meaningless null pointer check before debugfs_remove_recursive

debugfs_remove_recursive() has taken the null pointer into account.  just
remove the null check before debugfs_remove_recursive().

Link: http://lkml.kernel.org/r/1537494404-16473-1-git-send-email-zhongjiang@huawei.com


Signed-off-by: zhong jiang <zhongjiang@huawei.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>