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/16a2442ea6ee896987a44df3ed509e4cfde44475.1714762038.git.namcao@linutronix.de
Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

Author: covanam

drivers/pci/hotplug/TODO

@@ -6,6 +6,8 @@ cpcihp:
   ->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
@@ -16,6 +18,8 @@ cpqphp:
 * 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:
 
 * Implementations of hotplug_slot_ops callbacks such as get_adapter_present()
@@ -43,6 +47,8 @@ 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:
 
 * Several functions access the pci_slot member in struct hotplug_slot even