leaudio: Fix invalid handling Enable state

If remote device would send twice Enable state on the second device
trying to get to streaming state, the state machine would call twice
CisCreateForDevice, which would lead to:

01-10 11:39:21.252865  2015  3201 I bt_stack: [INFO:state_machine.cc(1316)] CisCreateForDevice cis handle: 97 acl handle : 0x00000041
01-10 11:39:21.266078  2015  3201 F bt_stack: [FATAL:btm_iso_impl.h(246)] Assert failed: !(cis->state_flags & (kStateFlagIsConnected | kStateFlagIsConnecting)). Already connected or connecting

This patch, fixes that by calling CisCreateForDevice only on transition
from QoSConfigured to Enabling state.

Bug: 264954923
Test: atest BluetoothInstrumentationTests
Tag: #feature
Change-Id: I30e8607c6b6a86b773ef642ffaeca1a881d8b931