dma-mapping: remove a pointless memset in dma_atomic_pool_init

We already zero the memory after allocating it from the pool that
this function fills, and having the memset here in this form means
we can't support CMA highmem allocations.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reported-by: Russell King - ARM Linux <linux@armlinux.org.uk>

kernel/dma/remap.c

@@ -121,7 +121,6 @@ int __init dma_atomic_pool_init(gfp_t gfp, pgprot_t prot)
 	if (!page)
 		goto out;
 
-	memset(page_address(page), 0, atomic_pool_size);
 	arch_dma_prep_coherent(page, atomic_pool_size);
 
 	atomic_pool = gen_pool_create(PAGE_SHIFT, -1);