[media] cx23885: Fix some smatch warnings

Make sure that it won't go past the config buffers

	drivers/media/pci/cx23885/cx23885-dvb.c:1733 dvb_register() warn: buffer overflow 'netup_xc5000_config' 2 <= s32max
	drivers/media/pci/cx23885/cx23885-dvb.c:1745 dvb_register() warn: buffer overflow 'netup_stv0367_config' 2 <= s32max
	drivers/media/pci/cx23885/cx23885-dvb.c:1752 dvb_register() warn: buffer overflow 'netup_xc5000_config' 2 <= s32max

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>