Fixed invalid memory access in DGA video driver (thanks ldb!)

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%40560

src/video/dga/SDL_dgavideo.c

@@ -474,7 +474,7 @@ SDL_Surface *DGA_SetVideoMode(_THIS, SDL_Surface *current,
 		SDL_SetError("Unable to switch to requested mode");
 		return(NULL);
 	}
-	DGA_visualClass = modes[i].visualClass;
+	DGA_visualClass = mode->mode.visualClass;
 	memory_base = (Uint8 *)mode->data;
 	memory_pitch = mode->mode.bytesPerScanline;