nv50/ir: only enable mul saturate on G200+

nv50/ir: only enable mul saturate on G200+

Commit 44673512a84 enabled support for saturating fmul. However
experimentally this does not seem to work on the older chips. Restrict
the feature to G200 (NVA0) and later.

Reported-by: Pierre Moreau <pierre.morrow@free.fr>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=90350
Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Tested-by: Pierre Moreau <pierre.morrow@free.fr>
Reviewed-by: Tobias Klausmann <tobias.johannes.klausmann@mni.thm.de>
Cc: mesa-stable@lists.freedesktop.org