ftrace: Fix function_graph duration spacing with 7-digits

ftrace: Fix function_graph duration spacing with 7-digits

Jungseok Lee noticed the following:

Currently, row's width of 7-digit duration numbers not aligned with
other cases like the following example.

 3) $ 3999884 us |      }
 3)               |      finish_task_switch() {
 3)   0.365 us    |        _raw_spin_unlock_irq();
 3)   3.333 us    |      }
 3) $ 3999976 us |    }
 3) $ 3999979 us |  } /* schedule */

As adding a single white space in case of 7-digit numbers, the format
could be unified easily as follows.

 3) $ 2237472 us  |      }
 3)               |      finish_task_switch() {
 3)   0.364 us    |        _raw_spin_unlock_irq();
 3)   3.125 us    |      }
 3) $ 2237556 us  |    }
 3) $ 2237559 us  |  } /* schedule */

Instead of making a special case for 7-digit numbers, the logic
of the len and the space loop is slightly modified to make the
two cases have the same format.

Link: http://lkml.kernel.org/r/1436626300-1679-2-git-send-email-jungseoklee85@gmail.com
Reported-by: Jungseok Lee <jungseoklee85@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>