pktcdvd: 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: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/block/pktcdvd.c

@@ -2822,8 +2822,7 @@ static int pkt_setup_dev(dev_t dev, dev_t* pkt_dev)
 out_mem2:
 	put_disk(disk);
 out_mem:
-	if (pd->rb_pool)
-		mempool_destroy(pd->rb_pool);
+	mempool_destroy(pd->rb_pool);
 	kfree(pd);
 out_mutex:
 	mutex_unlock(&ctl_mutex);