drm/omap: use true,false for bool variable

Fixes coccicheck warning:

drivers/gpu/drm/omapdrm/displays/panel-dsi-cm.c:681:1-15: WARNING: Assignment of 0/1 to bool variable
drivers/gpu/drm/omapdrm/displays/panel-dsi-cm.c:732:1-15: WARNING: Assignment of 0/1 to bool variable

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zheng Bin <zhengbin13@huawei.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1579763123-62749-1-git-send-email-zhengbin13@huawei.com