hw/pci: fix crash on shpc error flow

If the pci bridge enters in error flow as part
of init process it will only delete the shpc mmio
subregion but not remove it from the properties list,
resulting in segmentation fault when the bridge runs
the exit function.

Example: add a pci bridge without specifing the chassis number:
    <qemu-bin> ... -device pci-bridge,id=p1
Result:
    (qemu) qemu-system-x86_64: -device pci-bridge,id=p1: Bridge chassis not specified. Each bridge is required to be assigned a unique chassis id > 0.
    qemu-system-x86_64: -device pci-bridge,id=p1: Device
    initialization failed.
    Segmentation fault (core dumped)

    if (child->class->unparent) {
    #0  0x00005555558d629b in object_finalize_child_property (obj=0x555556d2e830, name=0x555556d30630 "shpc-mmio[0]", opaque=0x555556a42fc8) at qom/object.c:1078
    #1  0x00005555558d4b1f in object_property_del_all (obj=0x555556d2e830) at qom/object.c:367
    #2  0x00005555558d4ca1 in object_finalize (data=0x555556d2e830) at qom/object.c:412
    #3  0x00005555558d55a1 in object_unref (obj=0x555556d2e830) at qom/object.c:720
    #4  0x000055555572c907 in qdev_device_add (opts=0x5555563544f0) at qdev-monitor.c:566
    #5  0x0000555555744f16 in device_init_func (opts=0x5555563544f0, opaque=0x0) at vl.c:2213
    #6  0x00005555559cf5f0 in qemu_opts_foreach (list=0x555555e0f8e0 <qemu_device_opts>, func=0x555555744efa <device_init_func>, opaque=0x0, abort_on_failure=1) at util/qemu-option.c:1057
    #7  0x000055555574a11b in main (argc=16, argv=0x7fffffffdde8, envp=0x7fffffffde70) at vl.c:423

Unparent the shpc mmio region as part of shpc cleanup.

Signed-off-by: Marcel Apfelbaum <marcel.a@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Amos Kong <akong@redhat.com>
