draw: Update for u_assembled_primitive -> u_assembled_prim rename.

draw: Update for u_assembled_primitive -> u_assembled_prim rename.

Mesa build is too complex to rely on successful builds. On refactorings
it is always a good idea to use git grep to prevent missing cases:

  $ git grep u_assembled_primitive
  src/gallium/auxiliary/draw/draw_pt_fetch_shade_pipeline_llvm.c:      u_assembled_primitive(in_prim);