V4L/DVB (10753): siano: convert EXPORT_SYMBOL to EXPORT_SYMBOL_GPL

As pointed out by Mauro Chehab, we should always use EXPORT_SYMBOL_GPL
instead of EXPORT_SYMBOL wherever possible.

A message was posted to the linux-media mailing list about this, checking
with Uri Shkolnik of Siano Mobile Silicon if this is okay to convert.

As per Uri's response to this email, it is OK for us to make this conversion.

http://www.spinics.net/lists/linux-media/msg02200.html

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