target/riscv: fix clzw implementation to operate on arg1

target/riscv: fix clzw implementation to operate on arg1

The refactored gen_clzw() uses ret as its argument, instead of arg1.
Fix it.

Signed-off-by: Philipp Tomsich <philipp.tomsich@vrull.eu>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210911140016.834071-3-philipp.tomsich@vrull.eu
Fixes: 60903915050 ("target/riscv: Add DisasExtend to gen_unary")
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>