perf probe: Annotate variable initialization

Annotate away this false positive warning on older GCCs:

    cc1: warnings being treated as errors
    builtin-probe.c: In function ‘parse_probe_event’:
    builtin-probe.c:72: warning: ‘nc’ is used uninitialized in this function

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Masami Hiramatsu <mhiramat@redhat.com>
LKML-Reference: <1257254947-16789-1-git-send-email-acme@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>