i965 gen6: Fix incorrect order of dwords in gen6_update_sol_indices()

i965 gen6: Fix incorrect order of dwords in gen6_update_sol_indices()

When updating SOL indices, we were accidentally putting the starting
index in dword 1 and the SVBI number to increment in dword 2--these
should be reversed.  Usually both of these values are zero, so we
didn't see any problem.  However, if a transform feedback operation
spans multiple batch buffers, the starting index will be nonzero.

Fixes piglit test "EXT_transform_feedback/intervening-read output".

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>