nixos/luksroot: sync the crypt-storage

Add a sync command just after writing to the /crypt-storage file in order to reduce
the possibilities of corruption errors.

Changed files
+1
nixos
modules
system
+1
nixos/modules/system/boot/luksroot.nix
···
if [ $? == 0 ]; then
echo -ne "$new_salt\n$new_iterations" > /crypt-storage${dev.yubikey.storage.path}
else
echo "Warning: Could not update LUKS key, current challenge persists!"
fi
···
if [ $? == 0 ]; then
echo -ne "$new_salt\n$new_iterations" > /crypt-storage${dev.yubikey.storage.path}
+
sync /crypt-storage${dev.yubikey.storage.path}
else
echo "Warning: Could not update LUKS key, current challenge persists!"
fi