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: 8ac919a0 ("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>