macfb: fix invalid object reference in macfb_common_realize()

During realize memory_region_init_ram_nomigrate() is used to initialise the RAM
memory region used for the framebuffer but the owner object reference is
incorrect since MacFbState is a typedef and not a QOM type.

Change the memory region owner to be the corresponding DeviceState to fix the
issue and prevent random crashes during macfb_common_realize().

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Fixes: 8ac919a0654 ("hw/m68k: add Nubus macfb video card")
Reviewed-by: BALATON Zoltan <balaton@eik.bme.hu>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20211007221253.29024-4-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

hw/display/macfb.c

@@ -365,7 +365,7 @@ static bool macfb_common_realize(DeviceState *dev, MacfbState *s, Error **errp)
     memory_region_init_io(&s->mem_ctrl, OBJECT(dev), &macfb_ctrl_ops, s,
                           "macfb-ctrl", 0x1000);
 
-    memory_region_init_ram_nomigrate(&s->mem_vram, OBJECT(s), "macfb-vram",
+    memory_region_init_ram_nomigrate(&s->mem_vram, OBJECT(dev), "macfb-vram",
                                      MACFB_VRAM_SIZE, &error_abort);
     s->vram = memory_region_get_ram_ptr(&s->mem_vram);
     s->vram_bit_mask = MACFB_VRAM_SIZE - 1;