xen/pt: Check for return values for xen_host_pci_[get|set] in init

and if we have failures we call xen_pt_destroy introduced in
'xen/pt: Move bulk of xen_pt_unregister_device in its own routine.'
and free all of the allocated structures.

Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
