igb: Replace rmb in Tx cleanup with read_barrier_depends

The rmb in the Tx cleanup path is a much stronger barrier than we really need.
All that is really needed is a read_barrier_depends since the location of the
EOP descriptor is dependent on the eop_desc value.
Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/igb/igb_main.c

@@ -5930,7 +5930,7 @@ static bool igb_clean_tx_irq(struct igb_q_vector *q_vector)
 			break;
 
 		/* prevent any other reads prior to eop_desc */
-		rmb();
+		read_barrier_depends();
 
 		/* if DD is not set pending work has not been completed */
 		if (!(eop_desc->wb.status & cpu_to_le32(E1000_TXD_STAT_DD)))