46f3f53b16
The refactor in cf9fcbf24e used the wrong area coordinate for the
clay brush: the original code used `ss->cache->location` as the
`area_co` passed to the bush callback, and the new code after refactor
used the `area_co` which was calculated as a displaced brush plane.
The calculation of the displaced brush area plane as `area_co` seems
to be unused, and reason for it is not really clear.
This change only restores the `area_co` passed to the brush callback
to the value it used to be prior to the refactor.
Pull Request: https://projects.blender.org/blender/blender/pulls/116738