igb: simplify swap in clean_rx_irq if using packet split

This update replaces the xchg calls that were added with a pair of
assignments as there is no need for the xchg calls and they were found to
cause issues on some architectures.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/igb/igb_main.c

@@ -3926,8 +3926,10 @@ send_up:
 		next_buffer = &rx_ring->buffer_info[i];
 
 		if (!(staterr & E1000_RXD_STAT_EOP)) {
-			buffer_info->skb = xchg(&next_buffer->skb, skb);
-			buffer_info->dma = xchg(&next_buffer->dma, 0);
+			buffer_info->skb = next_buffer->skb;
+			buffer_info->dma = next_buffer->dma;
+			next_buffer->skb = skb;
+			next_buffer->dma = 0;
 			goto next_desc;
 		}