i40e: Use a local variable for readability

Use a local variable to make the code a bit more readable.
Signed-off-by: Jan Sokolowski <jan.sokolowski@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40e/i40e_txrx.c

@@ -3528,6 +3528,7 @@ static int i40e_xmit_xdp_ring(struct xdp_frame *xdpf,
 	u16 i = xdp_ring->next_to_use;
 	struct i40e_tx_buffer *tx_bi;
 	struct i40e_tx_desc *tx_desc;
+	void *data = xdpf->data;
 	u32 size = xdpf->len;
 	dma_addr_t dma;
 
@@ -3535,8 +3536,7 @@ static int i40e_xmit_xdp_ring(struct xdp_frame *xdpf,
 		xdp_ring->tx_stats.tx_busy++;
 		return I40E_XDP_CONSUMED;
 	}
-
-	dma = dma_map_single(xdp_ring->dev, xdpf->data, size, DMA_TO_DEVICE);
+	dma = dma_map_single(xdp_ring->dev, data, size, DMA_TO_DEVICE);
 	if (dma_mapping_error(xdp_ring->dev, dma))
 		return I40E_XDP_CONSUMED;