[media] stk1160: Allow to change input while streaming

Remove the check as there's no reason to prevent the input from
being set when the device is streaming. This allows surveillance
applications (such as motion, zoneminder, etc.) to configure the
input while streaming.

Reported-by: Sergey 'Jin' Bostandzhyan <jin@mediatomb.cc>
Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>