ksym_tracer: Fix the output of stat tracing

- make ksym_tracer_stat_start() return head->first instead of
  &head->first
- make the output properly aligned

Before:

   Access type                Symbol                     Counter
     NA                   <NA>                              0
     RW                   pid_max                               0

After:

  Access Type   Symbol                                       Counter
  -----------   ------                                       -------
  RW            pid_max                                            0

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: "K.Prasad" <prasad@linux.vnet.ibm.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <4A52E346.5050608@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>