qemuBuildDiskDeviceStr: Use XML disk bus type names in error message

There's no point using the qemu-specific disk bus names in the error
message.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

src/qemu/qemu_command.c

@@ -1581,7 +1581,6 @@ qemuBuildDiskDeviceStr(const virDomainDef *def,
                        virQEMUCapsPtr qemuCaps)
 {
     g_auto(virBuffer) opt = VIR_BUFFER_INITIALIZER;
-    const char *bus = virDomainDiskQEMUBusTypeToString(disk->bus);
     const char *contAlias;
     g_autofree char *backendAlias = NULL;
     g_autofree char *scsiVPDDeviceId = NULL;
@@ -1838,7 +1837,8 @@ qemuBuildDiskDeviceStr(const virDomainDef *def,
     case VIR_DOMAIN_DISK_BUS_LAST:
     default:
         virReportError(VIR_ERR_INTERNAL_ERROR,
-                       _("unsupported disk bus '%s' with device setup"), bus);
+                       _("unsupported disk bus '%s' with device setup"),
+                       NULLSTR(virDomainDiskBusTypeToString(disk->bus)));
         return NULL;
     }