dmaengine: drop null test before destroy functions

Remove unneeded NULL test.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@@ expression x; @@
-if (x != NULL)
  \(kmem_cache_destroy\|mempool_destroy\|dma_pool_destroy\)(x);
// </smpl>
Signed-off-by: NJulia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: NVinod Koul <vinod.koul@intel.com>

drivers/dma/dmaengine.c

@@ -1066,11 +1066,9 @@ static void dmaengine_destroy_unmap_pool(void)
 	for (i = 0; i < ARRAY_SIZE(unmap_pool); i++) {
 		struct dmaengine_unmap_pool *p = &unmap_pool[i];
 
-		if (p->pool)
-			mempool_destroy(p->pool);
+		mempool_destroy(p->pool);
 		p->pool = NULL;
-		if (p->cache)
-			kmem_cache_destroy(p->cache);
+		kmem_cache_destroy(p->cache);
 		p->cache = NULL;
 	}
 }