rtc: sc27xx: Remove unnecessary conversion to bool

Here we could use the '!=' expression to fix the following coccicheck
warning:

./drivers/rtc/rtc-sc27xx.c:566:50-55: WARNING: conversion to bool not needed here

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/1604647854-876-1-git-send-email-kaixuxia@tencent.com