target/riscv: Don't modify SUM with is_debug

target/riscv: Don't modify SUM with is_debug

If we want to give the debugger a greater view of memory than
the cpu, we should simply disable the access check entirely,
not simply for this one corner case.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Weiwei Li <liweiwei@iscas.ac.cn>
Tested-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-Id: <20230325105429.1142530-23-richard.henderson@linaro.org>
Message-Id: <20230412114333.118895-23-richard.henderson@linaro.org>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>