perf annotate: Fix build on 32 bit for BPF annotation

Commit 6987561c

 ("perf annotate: Enable annotation of BPF programs") adds
support for BPF programs annotations but the new code does not build on 32-bit.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Acked-by: Song Liu <songliubraving@fb.com>
Fixes: 6987561c

 ("perf annotate: Enable annotation of BPF programs")
Link: http://lkml.kernel.org/r/20190403194452.10845-1-cascardo@canonical.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>