ofono_client: fix use of raise_exn

method raise_exn was removed in
1a7a3f0e4318bccbd3ed177d5b07fa3618d06868, but due to merge process it
remaine dbeing used in some places.

Change-Id: I89f4abe3d69aa4e7bc1fd6c6fd7e9fdea2cd8d19
diff --git a/src/osmo_gsm_tester/ofono_client.py b/src/osmo_gsm_tester/ofono_client.py
index 138f7df..45a4294 100644
--- a/src/osmo_gsm_tester/ofono_client.py
+++ b/src/osmo_gsm_tester/ofono_client.py
@@ -398,7 +398,7 @@
 
     def schedule_scan_register(self, mcc_mnc):
         if self.register_attempts > NETREG_MAX_REGISTER_ATTEMPTS:
-            self.raise_exn('Failed to find Network Operator', mcc_mnc=mcc_mnc, attempts=self.register_attempts)
+            raise log.Error('Failed to find Network Operator', mcc_mnc=mcc_mnc, attempts=self.register_attempts)
         self.register_attempts += 1
         netreg = self.dbus.interface(I_NETREG)
         self.dbg('Scanning for operators...')
@@ -473,7 +473,7 @@
     def connect(self, mcc_mnc=None):
         'Connect to MCC+MNC'
         if (mcc_mnc is not None) and (len(mcc_mnc) != 2 or None in mcc_mnc):
-            self.raise_exn('mcc_mnc value is invalid. It should be None or contain both valid mcc and mnc values:', mcc_mnc=mcc_mnc)
+            raise log.Error('mcc_mnc value is invalid. It should be None or contain both valid mcc and mnc values:', mcc_mnc=mcc_mnc)
         self.power_cycle()
         self.register_attempts = 0
         if self.is_connected(mcc_mnc):