nfsd: 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);
x = NULL;
-}
// </smpl>

Signed-off-by: Julia Lawall <[e-mail]>
Signed-off-by: J. Bruce Fields <[e-mail]>

fs/nfsd/nfscache.c

···
 	drc_hashtbl = NULL;
 	drc_hashsize = 0;
 
-	if (drc_slab) {
-		kmem_cache_destroy(drc_slab);
-		drc_slab = NULL;
-	}
+	kmem_cache_destroy(drc_slab);
+	drc_slab = NULL;
 }
 
 /*