tbf/test: Fix old_tbf argument to tbf_alloc_ul_tbf

Currently the ul_tbf is used in its own declaration as an argument to
tbf_alloc_ul_tbf, where dl_tbf can be used instead and makes more
sense.

This commit uses dl_tbf instead of ul_tbf as old_tbf.

Addresses:
  tbf/TbfTest.cpp:71:14: warning: ‘ul_tbf’ may be used uninitialized in
      this function

Sponsored-by: On-Waves ehf
1 file changed