In vp9_pick_inter_mode(), instead of using
vp9_get_pred_context_switchable_interp(xd) to assign filter_ref,
we use a less strict condition on assigning filter_ref.
This is to reduce the probabily of entering the flow of not
assigning filter_ref and then skipping filter search.

Overall PSNR gain 0.074% for rtc dataset

Details:
Low    Mid     High
0.185% -0.008% -0.082%

Change-Id: Id5c5ab38d3766c213d5681e17b4d1afd1529e676