csis: Fix active scan for set member

Scanning sessin was incoretly closed after first device found, no matter
if it belongs to the group or not. This is incorrect and this patch
fixes it.

Bug: 150670922
Tag: #feature
Sponsor: jpawlowski@
Test: atest --host bluetooth_csis_test

Change-Id: Iafc16e2cbb9e670bd21d6a44283fb03b39d46b67