perf_counter tools: Fix warn_unused_result warnings

Fix warnings for return values that we don't care about:

 util/quote.c:222: attention : ignoring return value of ‘fwrite’, declared with attribute warn_unused_result
 util/quote.c:235: attention : ignoring return value of ‘fwrite’, declared with attribute warn_unused_result
 util/quote.c: In function ‘write_name_quotedpfx’:
 util/quote.c:290: attention : ignoring return value of ‘fwrite’, declared with attribute warn_unused_result

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: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <1244146558-8635-1-git-send-email-fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>