drivers/dma: Eliminate a NULL pointer dereference

If td_desc is NULL, just skip both kfrees.

A simplified version of the semantic match that finds this problem is as
follows: (http://coccinelle.lip6.fr/)

// <smpl>
@r exists@
expression E,E1;
identifier f;
statement S1,S2,S3;
@@

if ((E == NULL && ...) || ...)
{
  ... when != if (...) S1 else S2
      when != E = E1
* E->f
  ... when any
  return ...;
}
else S3
// </smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/dma/timb_dma.c

@@ -382,7 +382,7 @@ static struct timb_dma_desc *td_alloc_init_desc(struct timb_dma_chan *td_chan)
 	td_desc = kzalloc(sizeof(struct timb_dma_desc), GFP_KERNEL);
 	if (!td_desc) {
 		dev_err(chan2dev(chan), "Failed to alloc descriptor\n");
-		goto err;
+		goto out;
 	}
 
 	td_desc->desc_list_len = td_chan->desc_elems * TIMB_DMA_DESC_SIZE;
@@ -410,7 +410,7 @@ static struct timb_dma_desc *td_alloc_init_desc(struct timb_dma_chan *td_chan)
 err:
 	kfree(td_desc->desc_list);
 	kfree(td_desc);
-
+out:
 	return NULL;
 
 }