ixgbe: 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: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/ixgbe/ixgbe_main.c

@@ -838,7 +838,7 @@ static bool ixgbe_clean_tx_irq(struct ixgbe_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(IXGBE_TXD_STAT_DD)))