Fix a typo in build_one_insn().

Fixes: b6bd53f9 ("MIPS: Add missing file for eBPF JIT.")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Cc: <stable@vger.kernel.org> # 4.13+
Patchwork: https://patchwork.linux-mips.org/patch/17491/Signed-off-by: James Hogan <jhogan@kernel.org>