target/riscv: Correct SXL return value for RV32 in RV64 QEMU

Ensure that riscv_cpu_sxl returns MXL_RV32 when runningRV32 in an
RV64 QEMU.

Signed-off-by: TANG Tiancheng <tangtiancheng.ttc@alibaba-inc.com>
Fixes: 05e6ca5e15 ("target/riscv: Ignore reserved bits in PTE for RV64")
Reviewed-by: Liu Zhiwei <zhiwei_liu@linux.alibaba.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20240919055048.562-4-zhiwei_liu@linux.alibaba.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
(cherry picked from commit 929e4277c1)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

target/riscv/cpu.h

@@ -647,8 +647,11 @@ static inline RISCVMXL riscv_cpu_sxl(CPURISCVState *env)
 #ifdef CONFIG_USER_ONLY
     return env->misa_mxl;
 #else
+    if (env->misa_mxl != MXL_RV32) {
         return get_field(env->mstatus, MSTATUS64_SXL);
+    }
 #endif
+    return MXL_RV32;
 }
 #endif