ubi: no NULL check needed before kmem_cache_destroy

kmem_cache_destroy calls free which checks for NULL.

Problem was indicated by coccinelle.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

drivers/mtd/ubi/attach.c

@@ -1205,8 +1205,7 @@ static void destroy_ai(struct ubi_attach_info *ai)
 		}
 	}
 
-	if (ai->aeb_slab_cache)
-		kmem_cache_destroy(ai->aeb_slab_cache);
+	kmem_cache_destroy(ai->aeb_slab_cache);
 
 	kfree(ai);
 }