perf config: Check not only section->from_system_config but also item's

perf config: Check not only section->from_system_config but also item's

Currently section->from_system_config is being checked multiple times.
item->from_system_config should be checked instead, when iterating thru
the items in a section. Fix it.

Signed-off-by: Taeung Song <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Namhyung Kim <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>