bpf, docs: Fix the code formatting in instruction-set

A minor typo fix to include "| BPF_LD" into its previous
code phrase:

``BPF_IND`` | BPF_LD --> ``BPF_IND | BPF_LD``

Signed-off-by: Shahab Vahedi <shahab@synopsys.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/b6120b31-3d1d-bf2d-2f2a-aa768d91257b@synopsys.com