[media] gspca_finepix: Remove unnecessary lock/unlock call

gspca_main: init_transfer does not do anything between calling sd_start
(which starts the workqueue) and releasing the usb_lock, so this
synchronization is a nop, remove it.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>