remove variables named B0 as it conflicts with ROOT B0() macro on mac OsX

Fixes a bug https://lxcbmredmine01.gsi.de/issues/2307

Semen found that on the Mac OsX one of the ROOT headers defines a macro named B0() This macro conflicts with B0 variables in the L1 tracker code. The solution is to not use "B0" as a variable name.