rtc: cpcap: Fix missing IRQF_ONESHOT as only threaded handler

Coccinelle noticed:
drivers/rtc/rtc-cpcap.c:271:7-32: ERROR: Threaded IRQ with no
primary handler requested without IRQF_ONESHOT
drivers/rtc/rtc-cpcap.c:287:7-32: ERROR: Threaded IRQ with no
primary handler requested without IRQF_ONESHOT

Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/1605000947-32882-1-git-send-email-tiantao6@hisilicon.com