usb: Make use of ktime_* comparison functions

Start using ktime_* compare functions to make the code backportable.
Now that may be a bit tricky due to recent change of ktime_t.

Signed-off-by: Mariusz Skamra <mariuszx.skamra@intel.com>
Acked-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@intel.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>