toolbox: fix build

Change-Id: I4d37ae4ad19620f77e37b739fb1248b712b3f986
Signed-off-by: Greg Hackmann <ghackmann@google.com>
diff --git a/toolbox/watchprops.c b/toolbox/watchprops.c
index 9921dbc..06cdebe 100644
--- a/toolbox/watchprops.c
+++ b/toolbox/watchprops.c
@@ -23,9 +23,9 @@
 
 static void announce(char *name, char *value)
 {
-    char *x;
+    unsigned char *x;
     
-    for(x = value; *x; x++) {
+    for(x = (unsigned char *)value; *x; x++) {
         if((*x < 32) || (*x > 127)) *x = '.';
     }