xen/pt: use address_space_memory object for memory region hooks

Commit 99605175 (xen-pt: Fix PCI devices re-attach failed) introduced
a subtle bug. As soon as the guest switches off Bus Mastering on the
device it immediately causes all the BARs be unmapped due to the DMA
address space of the device being changed. This is undesired behavior
because the guest may try to communicate with the device after that
which triggers the following errors in the logs:

[00:05.0] xen_pt_bar_read: Error: Should not read BAR through QEMU. @0x0000000000000200
[00:05.0] xen_pt_bar_write: Error: Should not write BAR through QEMU. @0x0000000000000200

The issue that the original patch tried to workaround (uneven number of
region_add/del calls on device attach/detach) was fixed in d25836ca
(memory: do explicit cleanup when remove listeners).
Signed-off-by: NIgor Druzhinin <igor.druzhinin@citrix.com>
Reported-by: NRoss Lagerwall <ross.lagerwall@citrix.com>
Acked-by: NAnthony PERARD <anthony.perard@citrix.com>
Signed-off-by: NStefano Stabellini <sstabellini@kernel.org>

hw/xen/xen_pt.c

@@ -907,7 +907,7 @@ out:
         }
     }
 
-    memory_listener_register(&s->memory_listener, &s->dev.bus_master_as);
+    memory_listener_register(&s->memory_listener, &address_space_memory);
     memory_listener_register(&s->io_listener, &address_space_io);
     s->listener_set = true;
     XEN_PT_LOG(d,