gianfar: Fix RXICr/TXICr programming for multi-queue mode

The correct behavior is to program the interrupt coalescing regs
(RXICr/TXICr) in accordance with the Rx/Tx Q's "rx/txcoalescing"
flag. That is, if the coalescing flag is 0 for a given Rx/Tx queue
then the corresponding coalescing register should be cleared.
This behavior is correctly implemented for the single-queue mode
(SQ_SG_MODE), but not for the multi-queue mode (MQ_MG_MODE).
This fixes the later case.

Signed-off-by: Claudiu Manoil <claudiu.manoil@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>