bsc: timelost_fsm: Remove unneeded set of out variable on failure

Documentation of the function explicitly states that the out
target_pchan param returns the "PCHAN waited for". If we return false,
then no PCHAN is being waited for. The 2 callers of this function only
use this out param if function returns true, so let's simplify the code.

Change-Id: Ib8f9b7e1f584dee885d6823dc043682577572bd8

src/osmo-bsc/timeslot_fsm.c

@@ -864,9 +864,6 @@ bool ts_is_lchan_waiting_for_pchan(struct gsm_bts_trx_ts *ts, enum gsm_phys_chan
 			return true;
 		}
 	}
-
-	if (target_pchan)
-		*target_pchan = ts->pchan_is;
 	return false;
 }