bts_osmo: Use correct parameters for create_pcu

Commit c9817a50ff8d4138f9659a4e6e146f9843662af1 moved code from
different BTS into a shared base class, and create_pcu method was
created to be implemented by subclasses to get a new pcu object.
However, parameters where wrongly copied over from pcu() method during
refactoring. create_pcu() has no parameters.

Change-Id: I1e95f2e658a870f86dd9d9d25f446b8efa4107a4
diff --git a/src/osmo_gsm_tester/bts_osmo.py b/src/osmo_gsm_tester/bts_osmo.py
index 16e79cf..f4210b8 100644
--- a/src/osmo_gsm_tester/bts_osmo.py
+++ b/src/osmo_gsm_tester/bts_osmo.py
@@ -84,7 +84,7 @@
 
     def pcu(self):
         if self._pcu is None:
-            self._pcu = self.create_pcu(self.suite_run, self, self.conf)
+            self._pcu = self.create_pcu()
         return self._pcu
 
     def set_bsc(self, bsc):