PCI: hotplug: Document unchecked return value of pci_hp_add_bridge()

Some hotplug drivers do not check the return value of pci_hp_add_bridge().
This may be problematic if the driver proceeds after pci_hp_add_bridge()
fails.

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Nam Cao <[e-mail]>
Signed-off-by: Bjorn Helgaas <[e-mail]>

drivers/pci/hotplug/TODO

···
   ->set_power callbacks in struct cpci_hp_controller_ops.  Why were they
   introduced?  Can they be removed from the struct?
 
+* Returned code from pci_hp_add_bridge() is not checked.
+
 cpqphp:
 
 * The driver spawns a kthread cpqhp_event_thread() which is woken by the
···
 
 * A large portion of cpqphp_ctrl.c and cpqphp_pci.c concerns resource
   management.  Doesn't this duplicate functionality in the core?
+
+* Returned code from pci_hp_add_bridge() is not checked.
 
 ibmphp:
 
···
 
 * A large portion of ibmphp_res.c and ibmphp_pci.c concerns resource
   management.  Doesn't this duplicate functionality in the core?
+
+* Returned code from pci_hp_add_bridge() is not checked.
 
 sgi_hotplug: