net: ethernet: stmmac: GMAC4.xx: Fix TX descriptor preparation

On GMAC4.xx each descriptor contains 2 buffers of 16KB (each).
Initially, those 2 buffers was filled in dwmac4_rd_prepare_tx_desc but
it is actually not needed. Indeed, stmmac driver supports frame up to
9000 bytes (jumbo). So only one buffer is needed.
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
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

@@ -254,14 +254,7 @@ static void dwmac4_rd_prepare_tx_desc(struct dma_desc *p, int is_fs, int len,
 {
 	unsigned int tdes3 = p->des3;
 
-	if (unlikely(len > BUF_SIZE_16KiB)) {
-		p->des2 |= (((len - BUF_SIZE_16KiB) <<
-			     TDES2_BUFFER2_SIZE_MASK_SHIFT)
-			    & TDES2_BUFFER2_SIZE_MASK)
-			    | (BUF_SIZE_16KiB & TDES2_BUFFER1_SIZE_MASK);
-	} else {
-		p->des2 |= (len & TDES2_BUFFER1_SIZE_MASK);
-	}
+	p->des2 |= (len & TDES2_BUFFER1_SIZE_MASK);
 
 	if (is_fs)
 		tdes3 |= TDES3_FIRST_DESCRIPTOR;