media: Fix typo in mixer_drv.c and hdmi_drv.c

Correct typo "sucessful" to "successful" in
drivers/media/video/s5p-tv/mixer_drv.c
drivers/media/video/s5p-tv/hdmi_drv.c

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>