media: bt8xx: avoid a useless memset

Avoid a memset after a call to 'dma_alloc_coherent()'.
This is useless since
commit 518a2f19 ("dma-mapping: zero memory returned from dma_alloc_*")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/pci/bt8xx/btcx-risc.c

@@ -73,7 +73,6 @@ int btcx_riscmem_alloc(struct pci_dev *pci,
 		dprintk("btcx: riscmem alloc [%d] dma=%lx cpu=%p size=%d\n",
 			memcnt, (unsigned long)dma, cpu, size);
 	}
-	memset(risc->cpu,0,risc->size);
 	return 0;
 }