media: imon: drop references only after device is no longer used

The point of using get/put_device() is to keep references
for as long as the device may be in use. That means dropping
them must be the penultimate action right before freeing the memory.

Signed-off-by: Oliver Neukum <oneukum@suse.com>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>