dma-mapping: use 'bitmap_zalloc()' when applicable

'dma_mem->bitmap' is a bitmap. So use 'bitmap_zalloc()' to simplify code,
improve the semantic and avoid some open-coded arithmetic in allocator
arguments.

Also change the corresponding 'kfree()' into 'bitmap_free()' to keep
consistency.
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Christoph Hellwig <hch@lst.de>

kernel/dma/coherent.c

@@ -40,7 +40,6 @@ static struct dma_coherent_mem *dma_init_coherent_memory(phys_addr_t phys_addr,
 {
 	struct dma_coherent_mem *dma_mem;
 	int pages = size >> PAGE_SHIFT;
-	int bitmap_size = BITS_TO_LONGS(pages) * sizeof(long);
 	void *mem_base;
 
 	if (!size)
@@ -53,7 +52,7 @@ static struct dma_coherent_mem *dma_init_coherent_memory(phys_addr_t phys_addr,
 	dma_mem = kzalloc(sizeof(struct dma_coherent_mem), GFP_KERNEL);
 	if (!dma_mem)
 		goto out_unmap_membase;
-	dma_mem->bitmap = kzalloc(bitmap_size, GFP_KERNEL);
+	dma_mem->bitmap = bitmap_zalloc(pages, GFP_KERNEL);
 	if (!dma_mem->bitmap)
 		goto out_free_dma_mem;
 
@@ -81,7 +80,7 @@ static void dma_release_coherent_memory(struct dma_coherent_mem *mem)
 		return;
 
 	memunmap(mem->virt_base);
-	kfree(mem->bitmap);
+	bitmap_free(mem->bitmap);
 	kfree(mem);
 }