bpf: Fix comment error in fixup_kfunc_call function

insn->imm for kfunc is the relative address of __bpf_call_base,
instead of __bpf_base_call, Fix the comment error.

Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
Link: https://lore.kernel.org/r/20221208013724.257848-1-yangjihong1@huawei.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>