pci hotplug core: add check of duplicate slot name

Fix the following errors reported by Jan C. Nordholz in
http://bugzilla.kernel.org/show_bug.cgi?id=10751.

kobject_add_internal failed for 2 with -EEXIST, don't try to register things with the same name in the same directory.
Pid: 1, comm: swapper Tainted: G        W 2.6.26-rc3 #1
 [<c0266980>] kobject_add_internal+0x140/0x190
 [<c0266afd>] kobject_init_and_add+0x2d/0x40
 [<c027bc91>] pci_hp_register+0x81/0x2f0
 [<c027fd07>] pciehp_probe+0x1a7/0x470
 [<c01b3b84>] sysfs_add_one+0x44/0xa0
 [<c01b3c1f>] sysfs_addrm_start+0x3f/0xb0
 [<c01b497a>] sysfs_create_link+0x8a/0xf0
 [<c0279570>] pcie_port_probe_service+0x50/0x80
 [<c02e0545>] driver_sysfs_add+0x55/0x70
 [<c02e0662>] driver_probe_device+0x82/0x180
 [<c02e07cc>] __driver_attach+0x6c/0x70
 [<c02dfe0a>] bus_for_each_dev+0x3a/0x60
 [<c05db2d0>] pcied_init+0x0/0x80
 [<c02e04e6>] driver_attach+0x16/0x20
 [<c02e0760>] __driver_attach+0x0/0x70
 [<c02e0341>] bus_add_driver+0x1a1/0x220
 [<c05db2d0>] pcied_init+0x0/0x80
 [<c02e09cd>] driver_register+0x4d/0x120
 [<c05db050>] ibm_acpiphp_init+0x0/0x190
 [<c0125aab>] printk+0x1b/0x20
 [<c05db2d0>] pcied_init+0x0/0x80
 [<c05db2de>] pcied_init+0xe/0x80
 [<c05c751a>] kernel_init+0x10a/0x300
 [<c0120138>] schedule_tail+0x18/0x50
 [<c0103b9a>] ret_from_fork+0x6/0x1c
 [<c05c7410>] kernel_init+0x0/0x300
 [<c05c7410>] kernel_init+0x0/0x300
 [<c010485b>] kernel_thread_helper+0x7/0x1c
 =======================
pci_hotplug: Unable to register kobject '2'<3>pciehp: pci_hp_register failed with error -22

Slot with the same name can be registered multiple times if shpchp or
pciehp driver is loaded after acpiphp is loaded because ACPI based
hotplug driver and Native OS hotplug driver trying to handle the same
physical slot. In this case, current pci_hotplug core will call
kobject_init_and_add() muliple time with the same name. This is the
cause of this problem. To fix this problem, this patch adds the check
into pci_hp_register() to see if the slot with the same name.

Signed-off-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: Kristen Carlson Accardi <kristen.c.accardi@intel.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>