[media] gspca: fix dev_open() error path

If v4l2_fh_open() fails in dev_open(), gspca_dev->module left locked.
The patch adds module_put(gspca_dev->module) on this path.
Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>