PCUIF_Codec port, do not return fn in f_PCUIF_tx_imm_ass_pch

The function f_PCUIF_tx_imm_ass_pch() retuns the frame number, that is
sent back from osmo-bts via PCUIF / gsm_pcu_if_data_cnf_dt. Since we are
about to remove this field from gsm_pcu_if_data_cnf_dt, lets no longer
access it here as well. Also the return code is never used anywhere in
the tests. (In osmo-pcu the fn parameter was used for logging only, in
osmo-bts it was set to constant 0)

Related: OS#5927
Change-Id: I0e5bad7a0d74e5032f2818f6fdf5b9b2ecb531cc
2 files changed