[media] c8sectpfe: Combine three checks into a single if block

The variable "tsin" was checked three times in a loop iteration of the
c8sectpfe_tuner_unregister_frontend() function.
This implementation detail could be improved by the combination of the
involved statements into a single if block so that this variable will be
checked only once there.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>