Return the correct HAL data type for HAL_DIAG_ANI_STATS.

I .. stupidly added code to return HAL_ANI_STATS to HAL_DIAG_ANI_STATS.
I discovered this in a noisy environment when the returned values were
enough to .. well, make everything terrible.

So - restore functionality.

Tested:

• AR5416 (uses the AR5212 HAL), in a /very/ noisy 2GHz environment. Enough to trigger ANI to get upset and generate useful data.