wiiu/render: Fix missing max texture size

According to https://www.x.org/docs/AMD/old/R6xx_R7xx_3D.pdf in section
1.3 (page 6), GX2 supports textures of up to 8192x8192 resolution.

Author: Mefiresu

src/render/wiiu/SDL_render_wiiu.c

@@ -360,8 +360,8 @@ SDL_RenderDriver WIIU_RenderDriver =
 
             SDL_PIXELFORMAT_ARGB2101010,
         },
-        .max_texture_width = 0,
-        .max_texture_height = 0,
+        .max_texture_width = 8192,
+        .max_texture_height = 8192,
     },
 };