rtc: rv8803: fix missing unlock on error in rv8803_set_time()

Add the missing unlock before return from function rv8803_set_time()
in the error handling case.

Fixes: f8176e0b ("rtc: rv8803: initialize registers on post-probe voltage loss")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220627080822.3881072-1-yangyingliang@huawei.com