acpi: simplify build_isa_devices_aml()

x86 machines can have a single ISA bus only.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>
Reviewed-by: NIgor Mammedov <imammedo@redhat.com>
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200619091905.21676-9-kraxel@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/i386/acpi-build.c

@@ -979,18 +979,14 @@ static void build_isa_devices_aml(Aml *table)
 {
     VMBusBridge *vmbus_bridge = vmbus_bridge_find();
     bool ambiguous;
-
-    Aml *scope = aml_scope("_SB.PCI0.ISA");
     Object *obj = object_resolve_path_type("", TYPE_ISA_BUS, &ambiguous);
+    Aml *scope;
 
-    if (ambiguous) {
-        error_report("Multiple ISA busses, unable to define IPMI ACPI data");
-    } else if (!obj) {
-        error_report("No ISA bus, unable to define IPMI ACPI data");
-    } else {
-        build_acpi_ipmi_devices(scope, BUS(obj), "\\_SB.PCI0.ISA");
-        isa_build_aml(ISA_BUS(obj), scope);
-    }
+    assert(obj && !ambiguous);
+
+    scope = aml_scope("_SB.PCI0.ISA");
+    build_acpi_ipmi_devices(scope, BUS(obj), "\\_SB.PCI0.ISA");
+    isa_build_aml(ISA_BUS(obj), scope);
 
     if (vmbus_bridge) {
         aml_append(scope, build_vmbus_device_aml(vmbus_bridge));