sysbus failed assert for xen_sysdev

[Jason Andryuk <jandryuk@xxxxxxxxx>]

Hi,

Running qemu devel for a Xen VM is failing an assert after the recent
"qdev: Rework how we plug into the parent bus" sysbus changes.

qemu-system-i386: hw/core/qdev.c:102: qdev_set_parent_bus: Assertion
`dc->bus_type && object_dynamic_cast(OBJECT(bus), dc->bus_type)'
failed.

dc->bus_type is "xen-sysbus" and it's the
`object_dynamic_cast(OBJECT(bus), dc->bus_type)` portion that fails
the assert.  bus seems to be "main-system-bus", I think:
(gdb) p *bus
$3 = {obj = {class = 0x55555636d780, free = 0x7ffff7c40db0 <g_free>,
properties = 0x5555563f7180, ref = 3, parent = 0x5555563fe980}, parent
= 0x0, name = 0x5555563fec60 "main-system-bus", ...

The call comes from hw/xen/xen-legacy-backend.c:706
sysbus_realize_and_unref(SYS_BUS_DEVICE(xen_sysdev), &error_fatal);

Any pointers on what needs to be fixed?

Thanks,
Jason