bcachefs: fix mempool double initialization

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/compress.c

@@ -596,11 +596,13 @@ static int __bch2_fs_compress_init(struct bch_fs *c, u64 features)
 			goto out;
 	}
 
+	if (!mempool_initialized(&c->decompress_workspace)) {
 		ret = mempool_init_kmalloc_pool(
 				&c->decompress_workspace,
 				1, decompress_workspace_size);
 		if (ret)
 			goto out;
+	}
 out:
 	pr_verbose_init(c->opts, "ret %i", ret);
 	return ret;