Support building with -Werror=strict-prototypes / -Werror=old-style-definition

Unfortunately "-std=c99" is not sufficient to make gcc ignore code that
uses constructs of earlier C standards, which were abandoned in C99.

See https://lwn.net/ml/fedora-devel/Y1kvF35WozzGBpc8@redhat.com/ for
some related discussion.

Change-Id: I84fd99442d0cc400fa562fa33623c142649230e2
diff --git a/utils/osmo-aka-verify.c b/utils/osmo-aka-verify.c
index bbc65ef..f23c349 100644
--- a/utils/osmo-aka-verify.c
+++ b/utils/osmo-aka-verify.c
@@ -88,7 +88,7 @@
 }
 
 
-static void help()
+static void help(void)
 {
 	printf( "Static SIM card parameters:\n"
 		"-k  --key\tSpecify Ki / K\n"