can-utils: fix unused variable warnings

As pointed out by Gary Bisson clang complains about unused variables in
some valid cases.

Reported-by: Gary Bisson <gary.bisson@boundarydevices.com>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>

bcmserver.c

@@ -135,7 +135,7 @@ void childdied(int i)
 	wait(NULL);
 }
 
-int main(int argc, char **argv)
+int main(void)
 {
 
 	int sl, sa, sc;