r600: don't set an index_bias for indirect draw calls

r600: don't set an index_bias for indirect draw calls

The bug #4657 mixed up which commit was actually responsible for
the regression, so re-apply this patch.

The indirect draw call already encodes the index bias so that no
additional encoding in the hardware is needed in this case.

This fixes a regression with a number of tests from
   dEQP-GLES31.functional.draw_indirect.random.*

Fixes: c6c532faa8cf172715b38783ec7175b626a63944
  "gallium/u_vbuf: use updated pipe_draw_start_count while using draw_vbo"

Closes #4671

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10388>