arm64: dma-mapping: Mark atomic_pool as __ro_after_init

atomic_pool is setup once while init stage and never changed after
that, so it is good candidate for __ro_after_init

Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/mm/dma-mapping.c

@@ -42,7 +42,7 @@ static pgprot_t __get_dma_pgprot(unsigned long attrs, pgprot_t prot,
 	return prot;
 }
 
-static struct gen_pool *atomic_pool;
+static struct gen_pool *atomic_pool __ro_after_init;
 
 #define DEFAULT_DMA_COHERENT_POOL_SIZE  SZ_256K
 static size_t atomic_pool_size __initdata = DEFAULT_DMA_COHERENT_POOL_SIZE;