fbdev: aty: use true, false for bool variables in atyfb_base.c

Fix the following coccicheck warning:

drivers/video/fbdev/aty/atyfb_base.c:3822:3-10: WARNING: Assignment of
0/1 to bool variable
drivers/video/fbdev/aty/atyfb_base.c:3824:3-9: WARNING: Assignment of
0/1 to bool variable

Signed-off-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200422071854.513-1-yanaijie@huawei.com