net: macb: remove extraneous return when MACB_EXT_DESC is defined

When macro MACB_EXT_DESC is defined we end up with two identical
return statements and just one is sufficient. Remove the extra
return.

Detected by CoverityScan, CID#1449361 ("Structurally dead code")
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Acked-by: NNicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/cadence/macb_main.c

@@ -146,7 +146,6 @@ static unsigned int macb_adj_dma_desc_idx(struct macb *bp, unsigned int desc_idx
 	default:
 		break;
 	}
-	return desc_idx;
 #endif
 	return desc_idx;
 }