PCI: pciehp: Use PCI_EXP_SLTCAP_PSN define

Use PCI_EXP_SLTCAP_PSN to make it easier to find code that uses the
Physical Slot Number field in the PCIe Slot Capabilities register.

No functional change.
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/hotplug/pciehp.h

@@ -127,7 +127,7 @@ struct controller {
 #define HP_SUPR_RM(ctrl)	((ctrl)->slot_cap & PCI_EXP_SLTCAP_HPS)
 #define EMI(ctrl)		((ctrl)->slot_cap & PCI_EXP_SLTCAP_EIP)
 #define NO_CMD_CMPL(ctrl)	((ctrl)->slot_cap & PCI_EXP_SLTCAP_NCCS)
-#define PSN(ctrl)		((ctrl)->slot_cap >> 19)
+#define PSN(ctrl)		(((ctrl)->slot_cap & PCI_EXP_SLTCAP_PSN) >> 19)
 
 int pciehp_sysfs_enable_slot(struct slot *slot);
 int pciehp_sysfs_disable_slot(struct slot *slot);