fix camera2DistortionCoef bug

[wujiazheng2020]

I find camera2DistortionCoef() function return the coef of cam1.
origin code:
Settings.cc Line 72:
cv::Mat camera2DistortionCoef() {return cv::Mat(vPinHoleDistorsion2_.size(),1,CV_32F,vPinHoleDistorsion1_.data());}

I change it to
cv::Mat camera2DistortionCoef() {return cv::Mat(vPinHoleDistorsion2_.size(),1,CV_32F,vPinHoleDistorsion2_.data());}

Tested in Euroc MH01-05, it is OK.