alx: Remove casts of pointer to same type

Casting a pointer to a pointer of the same type is pointless,
so remove these unnecessary casts.

Done via coccinelle script:

$ cat typecast_2.cocci
@@
type T;
T *foo;
@@

-	(T *)foo
+	foo
Signed-off-by: NJoe Perches <joe@perches.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/atheros/alx/main.c

@@ -535,7 +535,7 @@ static int alx_alloc_descriptors(struct alx_priv *alx)
 	if (!alx->descmem.virt)
 		goto out_free;
 
-	alx->txq.tpd = (void *)alx->descmem.virt;
+	alx->txq.tpd = alx->descmem.virt;
 	alx->txq.tpd_dma = alx->descmem.dma;
 
 	/* alignment requirement for next block */