net: stmmac: use correct define to get rx timestamp on GMAC4

In dwmac4_wrback_get_rx_timestamp_status we looking for a RX timestamp.
For that receive descriptors are handled and so we should use defines
related to receive descriptors. It'll no change the functional behavior
as RDES3_RDES1_VALID=TDES3_RS1V=BIT(26) but it makes code easier to read.
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c

@@ -268,7 +268,7 @@ static int dwmac4_wrback_get_rx_timestamp_status(void *desc, void *next_desc,
 	int ret = -EINVAL;
 
 	/* Get the status from normal w/b descriptor */
-	if (likely(p->des3 & TDES3_RS1V)) {
+	if (likely(le32_to_cpu(p->des3) & RDES3_RDES1_VALID)) {
 		if (likely(le32_to_cpu(p->des1) & RDES1_TIMESTAMP_AVAILABLE)) {
 			int i = 0;