'err' is known to be <0 at this point.

So, some cases can not be reached because of a missing "-".
Add it.

Fixes: ca2045e0 ("Bluetooth: Add bt_status")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>