xen_pt_pmcsr_reg_write() needs an adjustment to deal with the RW1C
nature of the not passed through bit 15 (PCI_PM_CTRL_PME_STATUS).
This is a preparatory patch for XSA-131.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>