fp: dont reference fragment.position.zw

progs/fp/position.txt

@@ -1,3 +1,4 @@
 !!ARBfp1.0
-MUL result.color, fragment.position, {.005}.x;
+MOV result.color, {0}.x;
+MUL result.color.xy, fragment.position, {.005}.x;
 END