init submodule script leaves gitconfig in modified state if submodule update fails

[colinschmidt]

Impact: software

Tell us about your environment:
Chipyard Version: 1.3

What is the current behavior?
If I have modifications in a submodule that would be updated by init-submodules-no-riscv-tools.sh the git submodule update command will fail and cause the script to exit early, leaving some of the git config *.update none commands to remain in effect.

What is the expected behavior?
The script should catch this error and return the git config back to the initial state before exiting