sfc: Correct efx_rx_buffer::page_offset when EFX_PAGE_IP_ALIGN != 0

RX DMA buffers start at an offset of EFX_PAGE_IP_ALIGN bytes from the
start of a cache line.  This offset obviously needs to be included in
the virtual address, but this was missed in commit b590ace09d51
('sfc: Fix efx_rx_buf_offset() in the presence of swiotlb') since
EFX_PAGE_IP_ALIGN is equal to 0 on both x86 and powerpc.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

drivers/net/ethernet/sfc/rx.c

@@ -215,7 +215,7 @@ static int efx_init_rx_buffers_page(struct efx_rx_queue *rx_queue)
 		rx_buf = efx_rx_buffer(rx_queue, index);
 		rx_buf->dma_addr = dma_addr + EFX_PAGE_IP_ALIGN;
 		rx_buf->u.page = page;
-		rx_buf->page_offset = page_offset;
+		rx_buf->page_offset = page_offset + EFX_PAGE_IP_ALIGN;
 		rx_buf->len = efx->rx_buffer_len - EFX_PAGE_IP_ALIGN;
 		rx_buf->flags = EFX_RX_BUF_PAGE;
 		++rx_queue->added_count;