Add missing double to float conversion, reported by Wim.

Fixes: http://savannah.cern.ch/bugs/?100433

PLEASE NOTE: There are quite a few missing TClingCallFunc conversions. I was/am
aware of them, however, I don't have any free cycles to fix them all now. I am
fixing one by one by demand until there is more time to spend on it.


git-svn-id: https://root.cern.ch/svn/root/trunk@48653 27541ba8-7e3a-0410-8455-c3a389f83636