Fix no-return-in-nonvoid-function ipaccess-auth.c:80

OBS post-build check complained:

Change-Id: Id1368f308f0af6ac88334002a8aa1e90737e563b
I: Program returns random data in a function
E: libtelnet no-return-in-nonvoid-function ipaccess-auth.c:80
diff --git a/util/ipaccess-auth.c b/util/ipaccess-auth.c
index e550f4a..e290acb 100644
--- a/util/ipaccess-auth.c
+++ b/util/ipaccess-auth.c
@@ -30,7 +30,7 @@
 }
 
 // nanoBTS Challenge/Response
-int ipaccess_telnet_auth(int sock)
+void ipaccess_telnet_auth(int sock)
 {
 	char buffer[512];
 	int rs;