bpf: Correct the comment about insn_to_jit_off

The insn_to_jit_off passed to bpf_prog_fill_jited_linfo should be the
first byte of the next instruction, or the byte off to the end of the
current instruction.

Signed-off-by: Pu Lehui <pulehui@huawei.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220530092815.1112406-4-pulehui@huawei.com