osmux: Remove extra newline from the osmux log message

<000b> osmux.c:177 Cannot find endpoint with cid=7
!
<000b> osmux.c:253 Cannot find an endpoint for circuit_id=7

The extra newline and '!' do not provide any extra value and
make reading the output more difficult. Just remove it.
diff --git a/openbsc/src/libmgcp/osmux.c b/openbsc/src/libmgcp/osmux.c
index f0c0c68..db5cee8 100644
--- a/openbsc/src/libmgcp/osmux.c
+++ b/openbsc/src/libmgcp/osmux.c
@@ -174,7 +174,7 @@
 			return tmp;
 	}
 
-	LOGP(DMGCP, LOGL_ERROR, "Cannot find endpoint with cid=%d\n!\n", cid);
+	LOGP(DMGCP, LOGL_ERROR, "Cannot find endpoint with cid=%d\n", cid);
 
 	return NULL;
 }