V4L/DVB: ivtv: sizeof() => ARRAY_SIZE()

This fixes a smatch warning:
drivers/media/video/ivtv/ivtv-vbi.c +138 ivtv_write_vbi(43)
	error: buffer overflow 'vi->cc_payload' 256 <= 1023

Signed-off-by: Dan Carpenter <error27@gmail.com>
Reviewed-by: Andy Walls <awalls@radix.net>
Signed-off-by: Andy Walls <awalls@radix.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>