SpriteBatch Effect Fix

This is a fix to an issue introduced in https://github.com/mono/MonoGame/pull/2824.

This restores the old behavior of the sprite effect only being applied once at `SpriteBatch.Setup()`.  This makes code like this...

```
spriteBatch.Begin();
effect.CurrentTechnique.Passes [0].Apply();
spriteBatch.Draw(myTexture, new Vector2 (100, 100), Color.White);
spriteBatch.End();
```

... work correctly again.  I verified this fix thru the unit tests which use this technique in several places.