bpf: Remove extra whitespace in SPDX tag for syscall/helpers man pages

There is an extra whitespace in the SPDX tag, before the license name,
in the script for generating man pages for the bpf() syscall and the
helpers. It has caused problems in Debian packaging, in the tool that
autodetects licenses. Let's clean it up.

Fixes: 5cb62b75 ("bpf, docs: Use SPDX license identifier in bpf_doc.py")
Signed-off-by: Alejandro Colomar <alx@kernel.org>
Signed-off-by: Quentin Monnet <quentin@isovalent.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20230411144747.66734-1-quentin@isovalent.com