glsl: Do not add extra padding to structures

glsl: Do not add extra padding to structures

This code was attemping to align the base of the structure to the required
alignment of the structure.  However, it had two problems:

1. It was aligning the target structure member, not the base of the
structure.

2. It was calculating the alignment based on the members previous to the
target member instead of all the members of the structure.

Fixes gles3conform failures in:

ES3-CTS.shaders.uniform_block.random.nested_structs.6
ES3-CTS.shaders.uniform_block.random.nested_structs_arrays_instance_arrays.2
ES3-CTS.shaders.uniform_block.random.nested_structs_arrays_instance_arrays.6
ES3-CTS.shaders.uniform_block.random.all_per_block_buffers.5
ES3-CTS.shaders.uniform_block.random.all_per_block_buffers.19
ES3-CTS.shaders.uniform_block.random.all_shared_buffer.0
ES3-CTS.shaders.uniform_block.random.all_shared_buffer.2
ES3-CTS.shaders.uniform_block.random.all_shared_buffer.6
ES3-CTS.shaders.uniform_block.random.all_shared_buffer.12

v2: Fix rebase failure noticed by Matt.

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