sysbus: Drop FROM_SYSBUS()

As a replacement, use your own macro based on OBJECT_CHECK().
Signed-off-by: NAndreas Färber <afaerber@suse.de>

include/hw/sysbus.h

@@ -55,9 +55,6 @@ struct SysBusDevice {
     pio_addr_t pio[QDEV_MAX_PIO];
 };
 
-/* Macros to compensate for lack of type inheritance in C.  */
-#define FROM_SYSBUS(type, dev) DO_UPCAST(type, busdev, dev)
-
 void *sysbus_new(void);
 void sysbus_init_mmio(SysBusDevice *dev, MemoryRegion *memory);
 MemoryRegion *sysbus_mmio_get_region(SysBusDevice *dev, int n);