PWGCF : Femtouniverse -- Fixing bug in dphi calculation

The extra factor of 0.1 that was scaling the magnetic field is removed. 
However, after removing this factor, the asin(<arg>) function for calculating dphi was blowing up at certain (mostly higher) values of radii. This is also taken care of by only allowing abs(<arg>) < 1.0.

Author: prchakra