qemu: Move 'done' label in qemuBuildControllerDevStr()

Even when we skip part of the processing, we still want error
checking on the buffer.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>

src/qemu/qemu_command.c

@@ -2801,10 +2801,10 @@ qemuBuildControllerDevStr(const virDomainDef *domainDef,
     if (qemuBuildDeviceAddressStr(&buf, domainDef, &def->info, qemuCaps) < 0)
         goto error;
 
+ done:
     if (virBufferCheckError(&buf) < 0)
         goto error;
 
- done:
     *devstr = virBufferContentAndReset(&buf);
     return 0;