bpftool: Fix prog object type in manpage

bpftool: Fix prog object type in manpage

bpftool's man page lists "program" as one of possible values for OBJECT,
while in fact bpftool accepts "prog" instead.

Reported-by: Jerry Snitselaar <jsnitsel@redhat.com>
Signed-off-by: Artem Savkov <asavkov@redhat.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Acked-by: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/bpf/20231103081126.170034-1-asavkov@redhat.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>