bcache: Use WARN_ONCE() instead of __WARN()

Signed-off-by: Kent Overstreet <koverstreet@google.com>
diff --git a/drivers/md/bcache/bset.c b/drivers/md/bcache/bset.c
index d4f2164..cb4578a 100644
--- a/drivers/md/bcache/bset.c
+++ b/drivers/md/bcache/bset.c
@@ -883,7 +883,7 @@
 		iter->data->k = bkey_next(iter->data->k);
 
 		if (iter->data->k > iter->data->end) {
-			__WARN();
+			WARN_ONCE(1, "bset was corrupt!\n");
 			iter->data->k = iter->data->end;
 		}