rtla/timerlat: Simplify "no value" printing on top

Instead of printing three times the same output, print it only once,
reducing lines and being sure that all no values have the same length.

It also fixes an extra '\n' when running the with kernel threads, like
here:

     =============== %< ==============
                                      Timer Latency

   0 00:00:01   |          IRQ Timer Latency (us)        |         Thread Timer Latency (us)
 CPU COUNT      |      cur       min       avg       max |      cur       min       avg       max
   2 #0         |        -         -         -         - |      161       161       161       161
   3 #0         |        -         -         -         - |      161       161       161       161
   8 #1         |       54        54        54        54 |        -         -         -         -'\n'

 ---------------|----------------------------------------|---------------------------------------
 ALL #1      e0 |                 54        54        54 |                161       161       161
     =============== %< ==============

This '\n' should have been removed with the user-space support that
added another '\n' if not running with kernel threads.

Link: https://lkml.kernel.org/r/0a4d8085e7cd706733a5dc10a81ca38b82bd4992.1713968967.git.bristot@kernel.org

Cc: stable@vger.kernel.org
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Juri Lelli <juri.lelli@redhat.com>
Fixes: cdca4f4e

 ("rtla/timerlat_top: Add timerlat user-space support")
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>