MIPS: lantiq: Use dma_zalloc_coherent() in dma code

Instead of using dma_alloc_coherent() and memset() directly use
dma_zalloc_coherent().

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/19962/
Cc: ralf@linux-mips.org
Cc: jhogan@kernel.org
Cc: john@phrozen.org
Cc: linux-mips@linux-mips.org
Cc: dev@kresin.me

arch/mips/lantiq/xway/dma.c

@@ -130,10 +130,9 @@ ltq_dma_alloc(struct ltq_dma_channel *ch)
 	unsigned long flags;
 
 	ch->desc = 0;
-	ch->desc_base = dma_alloc_coherent(NULL,
+	ch->desc_base = dma_zalloc_coherent(NULL,
 				LTQ_DESC_NUM * LTQ_DESC_SIZE,
 				&ch->phys, GFP_ATOMIC);
-	memset(ch->desc_base, 0, LTQ_DESC_NUM * LTQ_DESC_SIZE);
 
 	spin_lock_irqsave(&ltq_dma_lock, flags);
 	ltq_dma_w32(ch->nr, LTQ_DMA_CS);