x86: ftrace: Fix the misleading comment for arch/x86/kernel/ftrace.c

Fix the misleading comment for arch/x86/kernel/ftrace.c that it
had used nop instead of jmp.
Signed-off-by: Li Bin <huawei.libin@huawei.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

arch/x86/kernel/ftrace.c

 /*
- * Code for replacing ftrace calls with jumps.
+ * Dynamic function tracing support.
  *
  * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
  *