perfcounter: Handle some IO return values

perfcounter: Handle some IO return values

Building perfcounter tools raises the following warnings:

 builtin-record.c: In function ‘atexit_header’:
 builtin-record.c:464: erreur: ignoring return value of ‘pwrite’, declared with attribute warn_unused_result
 builtin-record.c: In function ‘__cmd_record’:
 builtin-record.c:503: erreur: ignoring return value of ‘read’, declared with attribute warn_unused_result

 builtin-report.c: In function ‘__cmd_report’:
 builtin-report.c:1403: erreur: ignoring return value of ‘read’, declared with attribute warn_unused_result

This patch handles these IO return values.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <1245456100-5477-1-git-send-email-fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>