media: stkwebcam: fix memory leak in stk_camera_probe

My local syzbot instance hit memory leak in usb_set_configuration().
The problem was in unputted usb interface. In case of errors after
usb_get_intf() the reference should be putted to correclty free memory
allocated for this interface.

Fixes: ec16dae5

 ("V4L/DVB (7019): V4L: add support for Syntek DC1125 webcams")
Cc: stable@vger.kernel.org
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>