USB: Refactor hub remote wake handling.

Refactor the code to check for a remote wakeup on a port into its own
function.  Keep the behavior the same, and set connect_change in
hub_events if the device disconnected on resume.  Cleanup references to
hdev->children[i-1] to use a common variable.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>