mesa: Do not list inactive block members as active

mesa: Do not list inactive block members as active

Fixes gles3conform failures in:

ES3-CTS.shaders.uniform_block.single_nested_struct.per_block_buffer_packed
ES3-CTS.shaders.uniform_block.single_nested_struct_array.per_block_buffer_packed
ES3-CTS.shaders.uniform_block.random.scalar_types.7
ES3-CTS.shaders.uniform_block.random.basic_arrays.4
ES3-CTS.shaders.uniform_block.random.basic_arrays.6
ES3-CTS.shaders.uniform_block.random.basic_instance_arrays.2
ES3-CTS.shaders.uniform_block.random.nested_structs.9
ES3-CTS.shaders.uniform_block.random.all_shared_buffer.3

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>