glsl: Fix unused value warning reported by Coverity

We don't use param in this part of the code, so no point in advancing
the pointer forward:

>>>     CID 1324983:  Code maintainability issues  (UNUSED_VALUE)
>>>     Assigning value from "param->get_next()" to "param" here, but that stored value is overwritten before it can be used.

Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>
1 file changed