Bluetooth: L2CAP: fix chan ref leak in l2cap_chan_timeout() on !conn

Bluetooth: L2CAP: fix chan ref leak in l2cap_chan_timeout() on !conn

__set_chan_timer() takes a l2cap_chan reference via l2cap_chan_hold()
before scheduling the delayed work.  The normal path in
l2cap_chan_timeout() drops this reference with l2cap_chan_put() at the
end, but the early return when chan->conn is NULL skips the put,
leaking the reference.

Add the missing l2cap_chan_put() before the early return.

Fixes: adf0398cee86 ("Bluetooth: l2cap: fix null-ptr-deref in l2cap_chan_timeout")
Cc: stable@vger.kernel.org
Signed-off-by: Siwei Zhang <oss@fourdim.xyz>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>