omapfb/dss: fix comparison to bool warning

Fix the following coccicheck warning:

drivers/video/fbdev/omap2/omapfb/dss/hdmi4.c:461:15-32: WARNING:
Comparison to bool
drivers/video/fbdev/omap2/omapfb/dss/dispc.c:891:5-35: WARNING:
Comparison of 0/1 to bool variable

Signed-off-by: Jason Yan <yanaijie@huawei.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Andrew F. Davis <afd@ti.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200422071903.637-1-yanaijie@huawei.com