bpf: Simplify assignment to struct bpf_insn pointer in do_misc_fixups()

bpf: Simplify assignment to struct bpf_insn pointer in do_misc_fixups()

In verifier.c, the following code patterns (in two places)
  struct bpf_insn *patch = &insn_buf[0];
can be simplified to
  struct bpf_insn *patch = insn_buf;
which is easier to understand.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20250703141106.1483216-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>