media: ddbridge: fix buffer overflow in max_set_input_unlocked()

Picked up code parts introduced one smatch error:

  drivers/media/pci/ddbridge/ddbridge-maxs8.c:163 max_set_input_unlocked() error: buffer overflow 'dev->link[port->lnr].lnb.voltage' 4 <= 255

Fix this by clamping the .lnb.voltage array access to 0-3 by "& 3"'ing
dvb->input.

Cc: Ralph Metzler <rjkm@metzlerbros.de>
Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>