lib/buildid: Fix build ID parsing logic

The parse_build_id_buf does not account Elf32_Nhdr header size
when getting the build id data pointer and returns wrong build
id data as result.

This is problem only for stable trees that merged 84887f4c
fix, the upstream build id code was refactored and returns proper
build id.

Acked-by: Andrii Nakryiko <andrii@kernel.org>
Fixes: 84887f4c ("lib/buildid: harden build ID parsing logic")
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>