bpf: Clean up indentation issue in BTF kflag processing

There is a statement that is indented one level too deeply, remove
the extraneous tab.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20190925093835.19515-1-colin.king@canonical.com