glsl: Fix a reference to UniformBlocks during uniform linking.

glsl: Fix a reference to UniformBlocks during uniform linking.

When converting var->location from pointing at the program's UniformBlocks to
pointing at the linked shader's UniformBlocks, I missed this change.  It
usually worked out in the end because the two lists happen to be the same in
many testcases.

Fixes a valgrind complaint on
oglconform ubo-compile.cpp advanced.std140.2stage

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>