glsl/tests: take refs on glsl types

glsl/tests: take refs on glsl types

Much like each driver, tests as standalone entities must take
references on the glsl types.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>