Engine: Replace SDL_RENDERER_ACCELERATED with SDL_RENDERER_SOFTWARE

We don't supported hardware accelerated rendering in any capacity
yet, so this definition breaks the port :^)
SDL_RENDERER_SOFTWARE ensures that SDL gives us a software based
renderer to draw to.

Author: Quaker762

src/linux/rw_sdl.c

@@ -562,7 +562,7 @@ static qboolean SWimp_InitGraphics( qboolean fullscreen )
         return false;
     }
 
-    renderer = SDL_CreateRenderer (window, -1, SDL_RENDERER_ACCELERATED);
+    renderer = SDL_CreateRenderer (window, -1, SDL_RENDERER_SOFTWARE);
     if (renderer == NULL) {
         Sys_Error("(SOFTSDL) SDL CreateRenderer failed: %s\n", SDL_GetError());
         return false;