USB: usbcore: Do not disable USB3 protocol ports in hub_activate()

When USB3 protocol port detects an USB3.0 device attach, the port will
automatically transition to the Enabled state upon the completion
of successful link training.

Do not disable USB3 protocol ports in hub_activate(), or USB3.0 device
will fail to be recognized if xHCI bus power management is implemented.

Signed-off-by: Andiry Xu <andiry.xu@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>