bpf: Remove insn_buf[] declaration in inner block

Two insn_buf[16] variables are declared in the function which acts on
function scope and block scope respectively. The statement in the inner
block is redundant, so remove it.

Signed-off-by: Jianlin Lv <Jianlin.Lv@arm.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210318024851.49693-1-Jianlin.Lv@arm.com