leaudio/vc/csis: Fix handling BTA_GATTC_ENC_CMPL_CB_EVT

Seems that BTA_GATTC_ENC_CMPL_CB_EVT is missing status of the
encryption, and it is called either on success or failure.

Note: Encryption is mandatory for Le Audio operations and profile shall
be disconnected if encryption is not enabled.

Bug: 233548307
Test: atest BluetoothInstrumentationTests

Change-Id: I8d8579cd1ae9d87275aa9e10e009f1296c2cb8cc
(cherry picked from commit 56d325e5)