Fix formatting in internal stats for vp10

This corrects a formatting error introduced in:
I1e9d548ce445d29002f0c59ebfd3957a6f15e702
where spaces were used as delimiters instead of tabs.

The corresponding fixes for vp9 and vp8 are in
Ibc4eb8fd82e6b926ba259a679dc98557cadba9b1.

Change-Id: Ica3d625d6672b3c47e0e208b45eede29b9004030