perf symbols: Ignore ABS symbols when loading data maps

When loading symbols in a data mapping, ABS symbols (which has a value
of SHN_ABS in its st_shndx) failed at elf_getscn().  And it marks the
loading as a failure so already loaded symbols cannot be fixed up.

I'm not sure what should be done. Just ignore them for now. :)

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1353502185-26521-19-git-send-email-eranian@google.com


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