nv50/ir: only avoid spilling constrained def if a mov is added

nv50/ir: only avoid spilling constrained def if a mov is added

fix spilling regression introduced by 5428066f5e

this is just a minor mistake done while moving the code out into a new
function. The function contained a loop which might have been terminated
earlier and skipped setting noSpill to 1. After the refactoring it was always
set.

Fixes: 5428066f5e1ef5ea6ae04c84019f270023cfc6aa
	("nv50/ir: make a copy of tex src if it's referenced multiple times")
Signed-off-by: Karol Herbst <kherbst@redhat.com>