[media] vmalloc_sg: off by one in error handling

The "i--" needs to happen at the start of the loop or it will try to
release something bogus (probably it will crash) and it won't release
the first ->vaddr_page[].

Fixes: 7b4eeed1 ('[media] vmalloc_sg: make sure all pages in vmalloc area are really DMA-ready')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

drivers/media/v4l2-core/videobuf-dma-sg.c

@@ -253,9 +253,11 @@ int videobuf_dma_init_kernel(struct videobuf_dmabuf *dma, int direction,
 	return 0;
 out_free_pages:
 	while (i > 0) {
-		void *addr = page_address(dma->vaddr_pages[i]);
-		dma_free_coherent(dma->dev, PAGE_SIZE, addr, dma->dma_addr[i]);
+		void *addr;
+
 		i--;
+		addr = page_address(dma->vaddr_pages[i]);
+		dma_free_coherent(dma->dev, PAGE_SIZE, addr, dma->dma_addr[i]);
 	}
 	kfree(dma->dma_addr);
 	dma->dma_addr = NULL;