hikey_idt should exit with a non-zero code on error

[axel-h]

hikey_idt should exit with a non-zero code on error. Seem it's always returning zero at the moment, which is a pain when using it in bigger scripts. See e.g. https://discuss.96boards.org/t/hikey960-recovery-hikey-idt-error/2322/11 for the error I'm running into, where it returns zero instead of an error

@Leo-Yan has forwarded this request to HiSilicon