Fix item 23197 (idol of the moon)

Fix bonus provided by druid item 23197 which was insanely high.


This commit [b2d8643](http://github.com/mangos-zero/server-old/commit/b2d8643) is one of those pending backports from old mangos-zero concatenated in: https://github.com/cmangos/issues/wiki/classic_backporting-todo-zero-commits

I tested it and this is my report:
> Without this commit, druids with item 23197 deals to much damage with moonfire spells. This commit fixes this.