lightnvm: pblk-gc: fix an error pointer dereference in init

These labels are reversed so we could end up dereferencing an error
pointer or leaking.

Fixes: 7f347ba6bb3a ("lightnvm: physical block device (pblk) target")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Matias Bjørling <matias@cnexlabs.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/lightnvm/pblk-gc.c

@@ -527,10 +527,10 @@ int pblk_gc_init(struct pblk *pblk)
 
 	return 0;
 
-fail_free_main_kthread:
-	kthread_stop(gc->gc_ts);
 fail_free_writer_kthread:
 	kthread_stop(gc->gc_writer_ts);
+fail_free_main_kthread:
+	kthread_stop(gc->gc_ts);
 
 	return ret;
 }