PCI hotplug: SGI hotplug: fix build failure

The commit bd3d99c1 ("PCI: Remove
untested Electromechanical Interlock (EMI) support in pciehp."), which
removes the definition of "struct hotplug_slot_attr", broke SGI
hotplug driver. By this commit, we get the following compile error.

drivers/pci/hotplug/sgi_hotplug.c:106: error: variable 'sn_slot_path_attr' has initializer but incomplete type
drivers/pci/hotplug/sgi_hotplug.c:106: error: unknown field 'attr' specified in initializer
drivers/pci/hotplug/sgi_hotplug.c:106: error: extra brace group at end of initializer
drivers/pci/hotplug/sgi_hotplug.c:106: error: (near initialization for 'sn_slot_path_attr')
drivers/pci/hotplug/sgi_hotplug.c:106: warning: excess elements in struct initializer
drivers/pci/hotplug/sgi_hotplug.c:106: warning: (near initialization for 'sn_slot_path_attr')
drivers/pci/hotplug/sgi_hotplug.c:106: error: unknown field 'show' specified in initializer
drivers/pci/hotplug/sgi_hotplug.c:106: warning: excess elements in struct initializer
drivers/pci/hotplug/sgi_hotplug.c:106: warning: (near initialization for 'sn_slot_path_attr')
drivers/pci/hotplug/sgi_hotplug.c: In function 'sn_hp_destroy':
drivers/pci/hotplug/sgi_hotplug.c:203: error: invalid use of undefined type 'struct hotplug_slot_attribute'
drivers/pci/hotplug/sgi_hotplug.c: In function 'sn_hotplug_slot_register':
drivers/pci/hotplug/sgi_hotplug.c:655: error: invalid use of undefined type 'struct hotplug_slot_attribute'

This patch fixes this regression by adding the definition of struct
hotplug_slot_attr into sgi_hotplug.c.
Tested-by: Mike Habeck <habeck@sgi.com>
Signed-off-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

drivers/pci/hotplug/sgi_hotplug.c

@@ -103,6 +103,12 @@ static ssize_t path_show (struct hotplug_slot *bss_hotplug_slot,
 	return retval;
 }
 
+struct hotplug_slot_attribute {
+	struct attribute attr;
+	ssize_t (*show)(struct hotplug_slot *, char *);
+	ssize_t (*store)(struct hotplug_slot *, const char *, size_t);
+};
+
 static struct hotplug_slot_attribute sn_slot_path_attr = __ATTR_RO(path);
 
 static int sn_pci_slot_valid(struct pci_bus *pci_bus, int device)