usb: acpi: Prevent null pointer dereference in usb_acpi_add_usb4_devlink()

In the Linux kernel, the following vulnerability has been resolved:

usb: acpi: Prevent null pointer dereference in usb_acpi_add_usb4_devlink()

As demonstrated by the fix for update_port_device_state,

commit 12783c0b9e2c ("usb: core: Prevent null pointer dereference in update_port_device_state"),

usb_hub_to_struct_hub() can return NULL in certain scenarios,

such as during hub driver unbind or teardown race conditions,

even if the underlying usb_device structure exists.

Plus, all other places that call usb_hub_to_struct_hub() in the same file

do check for NULL return values.

If usb_hub_to_struct_hub() returns NULL, the subsequent access to

hub->ports[udev->portnum - 1] will cause a null pointer dereference.