Fix two erroneous replacements with x_chance_in_y(). The rest were

correct.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@6429 c06c8d41-db1a-0410-9941-cceddc491573

Created by  j-p-e-g  on July 6, 2008
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