A clip grad fix for sparse tensors. (#7257)

diff --git a/torch/nn/utils/clip_grad.py b/torch/nn/utils/clip_grad.py
index 810b662..2876239 100644
--- a/torch/nn/utils/clip_grad.py
+++ b/torch/nn/utils/clip_grad.py
@@ -31,7 +31,7 @@
     clip_coef = max_norm / (total_norm + 1e-6)
     if clip_coef < 1:
         for p in parameters:
-            p.grad.data.mul_(clip_coef)
+            p.grad.data.mul_(clip_coef.item())
     return total_norm