toolbox: fix build

Change-Id: I4d37ae4ad19620f77e37b739fb1248b712b3f986
Signed-off-by: Greg Hackmann <ghackmann@google.com>
diff --git a/toolbox/insmod.c b/toolbox/insmod.c
index fb1448b..d252433 100644
--- a/toolbox/insmod.c
+++ b/toolbox/insmod.c
@@ -73,7 +73,7 @@
 		char *ptr = opts;
 
 		for (i = 2; (i < argc) && (ptr < end); i++) {
-			len = MIN(strlen(argv[i]), end - ptr);
+			len = MIN(strlen(argv[i]), (size_t)(end - ptr));
 			memcpy(ptr, argv[i], len);
 			ptr += len;
 			*ptr++ = ' ';