ARM: dma-mapping: fix build warning in __dma_alloc()

Fix build warning in __dma_alloc() as below:

arch/arm/mm/dma-mapping.c: In function '__dma_alloc':
arch/arm/mm/dma-mapping.c:653:29: warning: 'page' may be used uninitialized in this function [-Wuninitialized]

Signed-off-by: Jingoo Han <[e-mail]>
Signed-off-by: Marek Szyprowski <[e-mail]>

arch/arm/mm/dma-mapping.c

···
 			 gfp_t gfp, pgprot_t prot, bool is_coherent, const void *caller)
 {
 	u64 mask = get_coherent_dma_mask(dev);
-	struct page *page;
+	struct page *page = NULL;
 	void *addr;
 
 #ifdef CONFIG_DMA_API_DEBUG