vp9: Fix to use last_q for resize check

vp9: Fix to use last_q for resize check

For temporal layers resize is only checked
on the base/TL0 frames. So rc->last_q should be used,
which because rc is in the layer context, rc->last_q
will correspond to the qindex on last TL0 frame.
In the previous code cm->base_qindex was used, which
would correspond to qindex on last encoded frame, which
is not TL0 when temporal_layers > 1.

Change-Id: Iaf86f7156d2d48ae99a1b34ad576d453d490e746