mmc: owl-mmc: use true and false for bool variables

Fix coccicheck warnings:

./owl-mmc.c:524:2-18: WARNING: Assignment of 0/1 to bool variable
./owl-mmc.c:528:2-18: WARNING: Assignment of 0/1 to bool variable

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zou Wei <zou_wei@huawei.com>
Link: https://lore.kernel.org/r/1604888706-63429-1-git-send-email-zou_wei@huawei.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>