V4L/DVB (8722): sms1xxx: fix typo in license header

This should have read, "GNU General Public License version 2"
rather than, "GNU General Public License version 3"

This was actually a typo mass-blunder -- this is not a change in licence,
as the code was always GPLv2.

Signed-off-by: Uri Shkolnik <uris@siano-ms.com>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>