drm/i915: use true,false for bool variable in intel_crt.c

Fixes coccicheck warning:

drivers/gpu/drm/i915/display/intel_crt.c:1066:1-28: WARNING: Assignment of 0/1 to bool variable
drivers/gpu/drm/i915/display/intel_crt.c:928:2-29: WARNING: Assignment of 0/1 to bool variable
drivers/gpu/drm/i915/display/intel_crt.c:443:2-29: WARNING: Assignment of 0/1 to bool variable

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Ma Feng <mafeng.ma@huawei.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1578013959-31486-4-git-send-email-mafeng.ma@huawei.com