Update on "[ET-VK] Minor improvement to q_linear op shader."

This diff contains a minor improvement to the q_linear op shader in the Vulkan backend for Executorch. The code changes in the q_8w_linear.glsl file include a change in position parameter from a 3-element u16vec3 to a 2-element u16vec2.

Differential Revision: [D68113154](https://our.internmc.facebook.com/intern/diff/D68113154/)

[ghstack-poisoned]

Author: trivedivivek