perf report: Add s390 diagnosic sampling descriptor size

On IBM z13 machine types 2964 and 2965 the descriptor
sizes for sampling and diagnostic sampling entries
might be missing in the trailer entry and are set to zero.

This leads to a perf report failure when processing diagnostic
sampling entries.

This patch adds missing descriptor sizes when the trailer entry
contains zero for these fields.

Output before:
  [root@s38lp82 perf]#  ./perf report --stdio | fgrep Samples
  0xabbf0 [0x8]: failed to process type: 68
  Error:
  failed to process sample
  [root@s38lp82 perf]#

Output after:
  [root@s38lp82 perf]#  ./perf report --stdio | fgrep Samples
  # Total Lost Samples: 0
  # Samples: 3K of event 'SF_CYCLES_BASIC_DIAG'
  # Samples: 162  of event 'CF_DIAG'
  [root@s38lp82 perf]#

Fixes: 2b1444f2

 ("perf report: Add raw report support for s390 auxiliary trace")

Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Reviewed-by: Hendrik Brueckner <brueckner@linux.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Link: http://lkml.kernel.org/r/20190211100627.85714-1-tmricht@linux.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>