BLE: Don't access freed buffer in log message

When GATT fail to write data on L2CAP, buffer is freed by L2CAP.
Accessing the buffer leads to fatal failure while printing the message info.

Test: BLE discover services and BT off test cases

Fixes: 73018520
Change-Id: I661398fd1321f6e68026b3720db4965fd6584d70
(cherry picked from commit 109b4980daca07798f6290b0d2bff20e7590b8c0)