net: lan966x: use library helper for freeing tx buffers

The library has the helper fdma_free_phys() for freeing physical FDMA
memory. Use it in the exit path.
Signed-off-by: Daniel Machon <daniel.machon@microchip.com>
Reviewed-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c

@@ -229,14 +229,9 @@ static int lan966x_fdma_tx_alloc(struct lan966x_tx *tx)
 static void lan966x_fdma_tx_free(struct lan966x_tx *tx)
 {
 	struct lan966x *lan966x = tx->lan966x;
-	struct fdma *fdma = &tx->fdma;
-	int size;
 
 	kfree(tx->dcbs_buf);
-
-	size = sizeof(struct fdma_dcb) * fdma->n_dcbs;
-	size = ALIGN(size, PAGE_SIZE);
-	dma_free_coherent(lan966x->dev, size, fdma->dcbs, fdma->dma);
+	fdma_free_coherent(lan966x->dev, &tx->fdma);
 }
 
 static void lan966x_fdma_tx_activate(struct lan966x_tx *tx)