mm/zsmalloc.c: fix build when CONFIG_COMPACTION=n

Fixes: 701d6785 ("mm/zsmalloc.c: fix race condition in zs_destroy_pool")
Link: http://lkml.kernel.org/r/201908251039.5oSbEEUT%25lkp@intel.comReported-by: Nkbuild test robot <lkp@intel.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Henry Burns <henrywolfeburns@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Jonathan Adams <jwadams@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/zsmalloc.c

@@ -2412,7 +2412,9 @@ struct zs_pool *zs_create_pool(const char *name)
 	if (!pool->name)
 		goto err;
 
+#ifdef CONFIG_COMPACTION
 	init_waitqueue_head(&pool->migration_wait);
+#endif
 
 	if (create_cache(pool))
 		goto err;