deree-de5000: Provide dev_clear()

deree-de5000: Provide dev_clear()

Devices for the deree-de5000 driver do have additional data attached to it
that needs to be freed when the device is freed. While the driver gets it
right for the cleanup() callback it does not implement a dev_clear()
callback, so the default dev_clear() implementation is used which will not
free the additional data. This will cause memory leaks when sr_dev_clear()
is called for this driver.

To fix this provide a dev_clear() implementation that frees the additional
data.

Signed-off-by: Lars-Peter Clausen <redacted>