rtc: da9063: Simplify bool comparison

Fix the following coccicheck warning:

./drivers/rtc/rtc-da9063.c:246:5-18: WARNING: Comparison to bool

Reported-by: Tosk Robot <tencent_os_robot@tencent.com>
Signed-off-by: Kaixu Xia <kaixuxia@tencent.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/1604649637-1014-1-git-send-email-kaixuxia@tencent.com