They won't have included the actual source code in the game release. Source is compiled to a binary as part of the release process; you don't want to have to distribute masses of pointless source code, or have people trivially reverse-engineer your game. This snippet is an OpenGL vertex shader, which is an exception to the above as it needs to be compiled by the player's GPU driver and therefore cannot be included as binary.
Incidentally, this code just maps a vertex position from Vita screenspace coordinates to the range (-1,1), and is presumably used for rendering the game's sprites to a simple OpenGL viewport.
You won't get anything particularly interesting out of modding shader code, other than maybe some funky visual effects (e.g. change line 11 and add a - sign, and BAM mirrored sprites!)
Interesting! I have zero experience with any code of that type (contrast to my experience with ASM and hex via romhacking), so I had no idea what I was looking at. Interesting how such a small snippet seems beyond the capabilities (or beyond the attention span) of many handheld/console-pc port devs