Fixes this smatch warning:

drivers/media/usb/as102/as102_usb_drv.c:306 as102_usb_release() warn: can 'as102_dev' even be NULL?

And indeed, as102_dev can never be NULL, so just drop the NULL check.
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>