V4L/DVB (13957): IR: Fix sysfs attributes declaration

This patch fixes the declaration of the sysfs attributes for IR's, which
must be a NULL-terminated array of struct attribute *.
Without this patch, my machine crashes when inserting a DVB card.

Signed-off-by: Francesco Lavra <francescolavra@interfree.it>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>