[media] si4713: print product number

Print the PN value, useful to check what chip the dev board has.

Signed-off-by: Eduardo Valentin <edubezval@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>