perf tests: Factor attr tests WRITE_ASS macro

Changing WRITE_ASS macro per Namhyung's comments, so the main usage case
takes only attr field name and format string.

Suggested-by: Namhyung Kim <namhyung.kim@lge.com>
Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1352130579-13451-3-git-send-email-jolsa@redhat.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>