hw/acpi: Dumb down acpi_table_add() stub

hw/acpi: Dumb down acpi_table_add() stub

The QERR_ macros are leftovers from the days of "rich" error objects.
We've been trying to reduce their remaining use.

acpi_table_add() is only ever called on behalf of CLI option
-acpitable.  Since qemu-options.hx sets @arch_mask to QEMU_ARCH_I386,
it is reachable only for these targets.  Since they provide a real
acpi_table_add(), the stub is unreachable.

There's no point in unreachable code keeping QERR_UNSUPPORTED alive.
Dumb it down to g_assert_not_reached().

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20230207075115.1525-7-armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Juan Quintela <quintela@redhat.com>