Fix OpenGL example's companion window textures

[thegreatpissant]

OpenGL example's companion window is rendering the R/L views upside down. This adjusts the texture coordinates so they rendering the textures right side up.

[cmbruns]

@jeremyselan @JoeLudwig please consider incorporating @thegreatpissant 's very simple pull request here. Have you looked at the on-monitor view for the hellovr_opengl sample? It seems sorta embarrassing to continue to not fix this, if you ask me.