target/riscv: Fixup setting GVA

target/riscv: Fixup setting GVA

In preparation for adding support for the illegal instruction address
let's fixup the Hypervisor extension setting GVA logic and improve the
variable names.

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Message-id: 20211220064916.107241-3-alistair.francis@opensource.wdc.com