rtc: rtctest: enabling UIE for a chip that doesn't support it returns EINVAL

Calling ioctl(..., RTC_UIE_ON, ...) without CONFIG_RTC_INTF_DEV_UIE_EMUL
either ends in rtc_update_irq_enable if rtc->uie_unsupported is true
or in __rtc_set_alarm in the if (!rtc->ops->set_alarm) branch. In both
cases the return value is -EINVAL. So check for that one instead of
ENOTTY.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>