i965: Allocate dummy slots for point sprites before computing VUE map.

i965: Allocate dummy slots for point sprites before computing VUE map.

Commit f0cecd43d6b6d moved the VUE map computation to be only once, at
VS compile time.  However, it did so in slightly the wrong place: it
made the one call to brw_vue_compute_map happen right before the
allocation of dummy slots for replaced point sprite coordinates, causing
a different VUE map to be generated (at least on Ironlake).

Fixes a regression in Piglit's point-sprite test on Ironlake.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=46489
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>