rtc: mt6397: drop free_irq of devm_ allocated irq

rtc: mt6397: drop free_irq of devm_ allocated irq

The devm_request_threaded_irq function allocates irq that is
released when a driver detaches. Thus, there is no reason to
explicitly call free_irq in probe function.

Fixes: 851b87148aa2 ("rtc: mt6397: improvements of rtc driver")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Link: https://lore.kernel.org/r/20191113021720.9527-1-weiyongjun1@huawei.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>