back to 2**10 for bert loss scaler (tinygrad#6934)

getting 2 NaN for this, revert back to 2**10

examples/mlperf/model_train.py

@@ -658,7 +658,7 @@ def train_bert():
   save_ckpt_dir      = config["SAVE_CKPT_DIR"]          = getenv("SAVE_CKPT_DIR", "./ckpts")
   init_ckpt          = config["INIT_CKPT_DIR"]          = getenv("INIT_CKPT_DIR", BASEDIR)
 
-  loss_scaler        = config["LOSS_SCALER"]            = getenv("LOSS_SCALER", 2.0**13 if dtypes.default_float == dtypes.float16 else 1.0)
+  loss_scaler        = config["LOSS_SCALER"]            = getenv("LOSS_SCALER", 2.0**10 if dtypes.default_float == dtypes.float16 else 1.0)
   decay              = config["DECAY"]                  = getenv("DECAY", 0.01)
   epsilon            = config["EPSILON"]                = getenv("EPSILON", 1e-6)
   poly_power         = config["POLY_POWER"]             = getenv("POLY_POWER", 1.0)