Copyright (C) 2017 - The LineageOS Project
If you're just cloning it just for building, then use the following command to save bandwidth & space.
git clone --single-branch --depth=1 https://github.com/LinuxPanda/android_vendor_xiaomi_rosy.git -b 9
If you need the entire commit history, then the usual single branch clone command.
git clone --single-branch https://github.com/LinuxPanda/android_vendor_xiaomi_rosy.git -b 9