bpftool: fix typo in bash-completion
_bpftool_get_map_names => _bpftool_get_prog_names for prog-attach|detach.
Fixes: 99f9863a0c45 ("bpftool: Match maps by name")
Cc: Paul Chaignon <paul.chaignon@orange.com>
Signed-off-by: Song Liu <songliubraving@fb.com>