Corrected SDL_HapticUpdateEffect() returning 0 instead of index of effect.

According to documentation in header and wiki the index should be returned.
This change may break existing programs which assume only 0 means a success.

src/haptic/SDL_haptic.c

@@ -530,7 +530,7 @@ SDL_HapticUpdateEffect(SDL_Haptic * haptic, int effect,
 
     SDL_memcpy(&haptic->effects[effect].effect, data,
                sizeof(SDL_HapticEffect));
-    return 0;
+    return effect;
 }