nilfs2: 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: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/nilfs2/super.c

@@ -1405,13 +1405,9 @@ static void nilfs_destroy_cachep(void)
 	 */
 	rcu_barrier();
 
-	if (nilfs_inode_cachep)
 	kmem_cache_destroy(nilfs_inode_cachep);
-	if (nilfs_transaction_cachep)
 	kmem_cache_destroy(nilfs_transaction_cachep);
-	if (nilfs_segbuf_cachep)
 	kmem_cache_destroy(nilfs_segbuf_cachep);
-	if (nilfs_btree_path_cache)
 	kmem_cache_destroy(nilfs_btree_path_cache);
 }