fix a warning in test/sparse.h
fix a warning in test/sparse.h

Zefz/eigen,Zefz/eigen,pthulhu/eigen,pasuka/eigen,ritsu1228/eigen,cjntaylor/eigen,TSC21/Eigen,pthulhu/eigen,TSC21/Eigen,pasuka/eigen,toastedcrumpets/eigen,pasuka/eigen,toastedcrumpets/eigen,TSC21/Eigen,toastedcrumpets/eigen,Zefz/eigen,cjntaylor/eigen,pthulhu/eigen,ROCmSoftwarePlatform/hipeigen,pthulhu/eigen,ritsu1228/eigen,ritsu1228/eigen,ritsu1228/eigen,TSC21/Eigen,cjntaylor/eigen,ROCmSoftwarePlatform/hipeigen,pasuka/eigen,ROCmSoftwarePlatform/hipeigen,Zefz/eigen,ROCmSoftwarePlatform/hipeigen,toastedcrumpets/eigen,pasuka/eigen,cjntaylor/eigen,pthulhu/eigen,ritsu1228/eigen