testhaptic: fix watcom "&array may not produce intended result" warning

(cherry-picked from commit d0220395294b63fc542e1cfac68289a77a09fb86)

test/testhaptic.c

@@ -106,7 +106,7 @@ main(int argc, char **argv)
     SDL_ClearError();
 
     /* Create effects. */
-    SDL_memset(&efx, 0, sizeof(efx));
+    SDL_memset(efx, 0, sizeof(efx));
     nefx = 0;
     supported = SDL_HapticQuery(haptic);