csis: Improve notification about member availability

With this patch, if group of devices is completed, and new device using
same SIRK will show up, it will not be reported to the upper layers.

This is becasue some devices, use same sirk when supporting multipoint.

Bug: 236212225
Test: atest BluetoothInstrumentationTests
Tag: #feature
Change-Id: I97d098729ab708e060da1539beed2f2cb4bdef06