video: uvesafb: use true,false for bool variables

Fix the following coccicheck warning:

drivers/video/fbdev/uvesafb.c:48:12-17: WARNING: Assignment of 0/1 to
bool variable
drivers/video/fbdev/uvesafb.c:1827:3-13: WARNING: Assignment of 0/1 to
bool variable
drivers/video/fbdev/uvesafb.c:1829:3-13: WARNING: Assignment of 0/1 to
bool variable
drivers/video/fbdev/uvesafb.c:1835:3-9: WARNING: Assignment of 0/1 to
bool variable
drivers/video/fbdev/uvesafb.c:1837:3-9: WARNING: Assignment of 0/1 to
bool variable
drivers/video/fbdev/uvesafb.c:1839:3-8: 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/20200422071845.403-1-yanaijie@huawei.com