target/riscv: Avoid env_archcpu() when reading RISCVCPUConfig

target/riscv: Avoid env_archcpu() when reading RISCVCPUConfig

Use riscv_cpu_cfg(env) instead of env_archcpu().cfg.

Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-Id: <20230309071329.45932-2-liweiwei@iscas.ac.cn>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>