ravb: Fix typo AVB->DMAC

Fix the typo AVB->DMAC in comment, as the code following the comment
is for DMAC on Gigabit Ethernet IP.
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Suggested-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/renesas/ravb_main.c

@@ -588,7 +588,7 @@ static int ravb_dmac_init_gbeth(struct net_device *ndev)
 	/* Descriptor format */
 	ravb_ring_format(ndev, RAVB_BE);
 
-	/* Set AVB RX */
+	/* Set DMAC RX */
 	ravb_write(ndev, 0x60000000, RCR);
 
 	/* Set Max Frame Length (RTC) */