vfio/pci: do not set the PCIDevice 'has_rom' attribute

vfio/pci: do not set the PCIDevice 'has_rom' attribute

PCI devices needing a ROM allocate an optional MemoryRegion with
pci_add_option_rom(). pci_del_option_rom() does the cleanup when the
device is destroyed. The only action taken by this routine is to call
vmstate_unregister_ram() which clears the id string of the optional
ROM RAMBlock and now, also flags the RAMBlock as non-migratable. This
was recently added by commit b895de502717 ("migration: discard
non-migratable RAMBlocks"), .

VFIO devices do their own loading of the PCI option ROM in
vfio_pci_size_rom(). The memory region is switched to an I/O region
and the PCI attribute 'has_rom' is set but the RAMBlock of the ROM
region is not allocated. When the associated PCI device is deleted,
pci_del_option_rom() calls vmstate_unregister_ram() which tries to
flag a NULL RAMBlock, leading to a SEGV.

It seems that 'has_rom' was set to have memory_region_destroy()
called, but since commit 469b046ead06 ("memory: remove
memory_region_destroy") this is not necessary anymore as the
MemoryRegion is freed automagically.

Remove the PCIDevice 'has_rom' attribute setting in vfio.

Fixes: b895de502717 ("migration: discard non-migratable RAMBlocks")
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>