selftests/bpf: fix test_sysctl_prog with alu32

Similar to commit b7a0d65d80a0 ("bpf, testing: Workaround a verifier failure for test_progs")
fix test_sysctl_prog.c as well.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
1 file changed