[TMVA] Fix bug caught by testMinimizationCpu
[TMVA] Fix bug caught by testMinimizationCpu

The variable fDropoutProbability in DNN/Layer is being initialized twice
in the constructor, ignoring the value passed in the initialization
list, which causes a bug that breaks TGradientDescent minimizer.

olifre/root,root-mirror/root,karies/root,agarciamontoro/root,agarciamontoro/root,bbockelm/root,simonpf/root,zzxuanyuan/root,olifre/root,BerserkerTroll/root,karies/root,BerserkerTroll/root,simonpf/root,davidlt/root,agarciamontoro/root,bbockelm/root,mhuwiler/rootauto,bbockelm/root,mhuwiler/rootauto,zzxuanyuan/root,root-mirror/root,karies/root,simonpf/root,olifre/root,agarciamontoro/root,simonpf/root,BerserkerTroll/root,karies/root,simonpf/root,olifre/root,olifre/root,simonpf/root,olifre/root,zzxuanyuan/root,root-mirror/root,simonpf/root,root-mirror/root,davidlt/root,BerserkerTroll/root,agarciamontoro/root,zzxuanyuan/root,karies/root,karies/root,BerserkerTroll/root,BerserkerTroll/root,BerserkerTroll/root,mhuwiler/rootauto,simonpf/root,davidlt/root,bbockelm/root,agarciamontoro/root,olifre/root,root-mirror/root,davidlt/root,zzxuanyuan/root,davidlt/root,olifre/root,mhuwiler/rootauto,karies/root,mhuwiler/rootauto,root-mirror/root,mhuwiler/rootauto,BerserkerTroll/root,mhuwiler/rootauto,agarciamontoro/root,zzxuanyuan/root,zzxuanyuan/root,root-mirror/root,bbockelm/root,davidlt/root,bbockelm/root,zzxuanyuan/root,karies/root,mhuwiler/rootauto,davidlt/root,simonpf/root,agarciamontoro/root,root-mirror/root,karies/root,olifre/root,mhuwiler/rootauto,davidlt/root,karies/root,zzxuanyuan/root,bbockelm/root,bbockelm/root,bbockelm/root,davidlt/root,mhuwiler/rootauto,root-mirror/root,zzxuanyuan/root,root-mirror/root,zzxuanyuan/root,simonpf/root,bbockelm/root,bbockelm/root,BerserkerTroll/root,karies/root,olifre/root,root-mirror/root,davidlt/root,davidlt/root,olifre/root,agarciamontoro/root,BerserkerTroll/root,agarciamontoro/root,zzxuanyuan/root,simonpf/root,agarciamontoro/root,mhuwiler/rootauto,BerserkerTroll/root