usb: hub: fix a typo in hub_port_init() leading to wrong logic

A typo of j for i led to a logic bug. To rule out future
confusion, the variable names are made meaningful.

Signed-off-by: Oliver Neukum <ONeukum@suse.com>
CC: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>