target/riscv/csr.c: avoid env_archcpu() usages when reading RISCVCPUConfig

target/riscv/csr.c: avoid env_archcpu() usages when reading RISCVCPUConfig

Retrieving the CPU pointer using env_archcpu() just to access cpu->cfg
can be avoided by using riscv_cpu_cfg().

Suggested-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Weiwei Li <liweiwei@iscas.ac.cn>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20230224174520.92490-5-dbarboza@ventanamicro.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>