[media] stk-webcam: fix querycap and simplify s_input

Add device_caps support to querycap, fill in bus_info correctly and
do not set the version field (let the core handle that).
Also simplify the s_input ioctl.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Tested-by: Arvydas Sidorenko <asido4@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>