selftests/bpf: Fix btf_dump padding test case

selftests/bpf: Fix btf_dump padding test case

[ Upstream commit 76790c7c66ccc8695afc75e73f54c0ca86267ed2 ]

Existing padding test case for btf_dump has a good test that was
supposed to test padding generation at the end of a struct, but its
expected output was specified incorrectly. Fix this.

Fixes: 2d2a3ad872f8 ("selftests/bpf: add btf_dump BTF-to-C conversion tests")
Reported-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20191008231009.2991130-4-andriin@fb.com
Signed-off-by: Sasha Levin <sashal@kernel.org>