libvpx

Properly reset the block coding skip flag array in non-RD mode

The block coding skip flags are assigned in the normal RD mode
decision loop. They are then used in the final encoding stage.
In the non-RD mode decision, the forward transform and quantization
stages are replaced by modeling based on SSE and variance of
prediction residues. This commit applies reset to this array in
the non-RD coding mode.

Change-Id: I66584669b035e9c8ac23e95047849ff277472742