glsl: Only set ir_variable::constant_value for const-decorated variables

Right now we're also setting for uniforms, and that doesn't seem to hurt
things.  The next patch will make general global variables in GLSL ES,
and those definitely should not have constant_value set!

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Cc: "10.6 11.0" <mesa-stable@lists.freedesktop.org>
1 file changed