fixed warnings in MSVC x64 compilation
diff --git a/tests/test_ppc.c b/tests/test_ppc.c
index f68ad7b..8748438 100644
--- a/tests/test_ppc.c
+++ b/tests/test_ppc.c
@@ -16,7 +16,7 @@
 
 static csh handle;
 
-static void print_string_hex(char *comment, unsigned char *str, int len)
+static void print_string_hex(char *comment, unsigned char *str, size_t len)
 {
 	unsigned char *c;