Commit a621f38d (Direct dispatch
through MemoryRegion) moved byte swaps to a central function.

Add a missing break, so that long-sized byte swaps don't abort.
Signed-off-by: NAndreas Färber <afaerber@suse.de>
Reviewed-by: NAurelien Jarno <aurelien@aurel32.net>
Signed-off-by: NAvi Kivity <avi@redhat.com>