samples/bpf: Fix fout leak in hbm's run_bpf_prog

Fix fout being fopen'ed but then not subsequently fclose'd. In the affected
branch, fout is otherwise going out of scope.

Signed-off-by: Hao Zeng <zenghao@kylinos.cn>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20230411084349.1999628-1-zenghao@kylinos.cn