For 1 pass: always use the normative filter in vp9_scale_if_required()

For 1 pass: always use the normative filter in vp9_scale_if_required()

The normative (convolve8) filter is optimized/faster than
the nonnormative one. Pass usage of scaler (normative/nonomorative)
to vp9_scale_if_required(), and always use normative one for 1 pass.

Change-Id: I2b71d9ff18b3c7499b058d1325a9554de993dd52