cutils: Simplify how parse_uint() checks for whitespace

Use qemu_isspace() so we don't have to cast to unsigned char.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20190514180311.16028-7-armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

util/cutils.c

@@ -683,7 +683,7 @@ int parse_uint(const char *s, unsigned long long *value, char **endptr,
     }
 
     /* make sure we reject negative numbers: */
-    while (isspace((unsigned char)*s)) {
+    while (qemu_isspace(*s)) {
         s++;
     }
     if (*s == '-') {