csis: Fix clearing temporary device for group verification

During set member pairing, there is additional verification of the SIRK
which happens after pairing.
This patch fixes possible issue which could lead to situation that
temporary device was not cleared properly

Bug: 294604632
Test: atest bluetooth_csis_test
Tag: #feature
Change-Id: I293d0a5b9c04001f974d76ee2140d52233b8e367