V4L/DVB: dib0700: properly implement IR change_protocol

This patch implements change_protocol callback. With this change,
there's no need for an extra modprobe parameter to specify the
protocol. When a table is loaded (either from in-kernel rc-map
tables or via ir-keytable program), the driver will automatically
change the protocol, in order to work with the given table.

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