virtio-ccw: do not include headers for all virtio devices

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
index 90480e7..2d32647 100644
--- a/hw/s390x/s390-virtio-ccw.c
+++ b/hw/s390x/s390-virtio-ccw.c
@@ -25,6 +25,7 @@
 #include "qemu/error-report.h"
 #include "qemu/option.h"
 #include "qemu/qemu-print.h"
+#include "qemu/units.h"
 #include "hw/s390x/s390-pci-bus.h"
 #include "sysemu/reset.h"
 #include "hw/s390x/storage-keys.h"