hw/riscv/virt.c: use g_autofree in virt_machine_init()

hw/riscv/virt.c: use g_autofree in virt_machine_init()

Move 'soc_name' to the loop, and give it g_autofree, to avoid the manual
g_free().

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20240122221529.86562-7-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>