glapi: fix param type in TexGenxOES
What does this MR do and why?
glapi: fix param type in TexGenxOES
The spec [1] and _mesa_TexGenxOES both agree that it's GLfixed
instead of GLint.
[1]: https://registry.khronos.org/OpenGL/extensions/OES/OES_texture_cube_map.txt