scripts: Ensure git config changes are reverted on failure

Fixes #595

scripts/init-fpga.sh

@@ -4,7 +4,7 @@ set -e
 set -o pipefail
 
 # Enable submodule update for FPGA tools.
-git config --unset submodule.fpga/fpga-shells.update
+git config --unset submodule.fpga/fpga-shells.update || :
 # Initialize local FPGA tools.
 git submodule update --init --recursive fpga/fpga-shells
 # Disable submodule update for FPGA tools.