taprio: calculate cycle_time when schedule is installed

cycle time for a particular schedule is calculated only when it is first
installed. So, it makes sense to just calculate it once right after the
'cycle_time' parameter has been parsed and store it in cycle_time.

Signed-off-by: Vedang Patel <vedang.patel@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>