mfd: dbx500-prcmu: Use true and false for bool variable

Fix the following coccicheck warning:

./include/linux/mfd/db8500-prcmu.h:723:8-9: WARNING: return of 0/1 in
function 'db8500_prcmu_is_ac_wake_requested' with return type bool.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>