net: dsa: hellcreek: Fix incorrect setting of GCL

Currently the gate control list which is programmed into the hardware is
incorrect resulting in wrong traffic schedules. The problem is the loop
variables are incremented before they are referenced. Therefore, move the
increment to the end of the loop.

Fixes: 24dfc6eb

 ("net: dsa: hellcreek: Add TAPRIO offloading support")
Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>