SDP: add return after SDP disconnection

A return is needed after sdp_disconnect(). It is the logic
expected and it prevents the use of p_ccb after it's freed.

Bug: 144177780
Bug: 117105007
Test: manual test
Change-Id: I7a64382b36adca37a8ff0c7e361d89ecdc8f3b55
(cherry picked from commit 30efc8c90a846460359a489e17e1461c725958b3)