decoder: h264: fix initialization of RefPicLists for multiple slices.

The initialization of reference picture lists (8.2.4.2) applies to all
slices. So, the RefPicList0/1 lists need to be constructed prior to
each slice submission to the HW decoder.

This fixes decoding of video sequences where frames are encoded with
multiple slices of different types, e.g. 4 slices in this order I, P,
I, and P. More precisely, CABAST3_Sony_E and CABASTBR3_Sony_B.