use PROGRAM_CONSTANT instead of PROGRAM_STATE_VAR when generating immediates/literals

(cherry picked from commit fdc8636bdc)

src/mesa/main/texenvprogram.c

@@ -595,7 +595,7 @@ static struct ureg register_const4f( struct texenv_fragment_program *p,
    idx = _mesa_add_unnamed_constant( p->program->Base.Parameters, values, 4,
                                      &swizzle );
    ASSERT(swizzle == SWIZZLE_NOOP);
-   return make_ureg(PROGRAM_STATE_VAR, idx);
+   return make_ureg(PROGRAM_CONSTANT, idx);
 }
 
 #define register_scalar_const(p, s0)    register_const4f(p, s0, s0, s0, s0)