[media] cx18: avoid going past input/audio array

As reported by smatch:
	drivers/media/pci/cx18/cx18-driver.c:807 cx18_init_struct2() error: buffer overflow 'cx->card->video_inputs' 6 <= 6

That happens because nof_inputs and nof_audio_inputs can be initialized
as CX18_CARD_MAX_VIDEO_INPUTS, instead of CX18_CARD_MAX_VIDEO_INPUTS - 1.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Acked-by: Andy Walls <awalls@md.metrocast.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>