BSC_Tests: fix DTE in TC_lost_sdcch_during_assignment()

This test case fails in ttcn3-bsc-test-sccplite due to:

  BSC_Tests.ttcn:10212 Dynamic test case error:
    Using the value of an optional field containing omit.

Change-Id: I235027c2b53b8f2ae975e25eb7c38b1959668d6f
Related: SYS#5627
1 file changed