char: cast ARRAY_SIZE() as signed to silent warning on empty array

chardev/char.c: In function 'chardev_name_foreach':
chardev/char.c:546:19: error: comparison of unsigned expression < 0 is always false [-Werror=type-limits]
     for (i = 0; i < ARRAY_SIZE(chardev_alias_table); i++) {
                   ^
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20170530120919.8874-1-f4bug@amsat.org>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>

chardev/char.c

@@ -841,7 +841,7 @@ chardev_name_foreach(void (*fn)(const char *name, void *opaque), void *opaque)
 
     object_class_foreach(chardev_class_foreach, TYPE_CHARDEV, false, &fe);
 
-    for (i = 0; i < ARRAY_SIZE(chardev_alias_table); i++) {
+    for (i = 0; i < (int)ARRAY_SIZE(chardev_alias_table); i++) {
         fn(chardev_alias_table[i].alias, opaque);
     }
 }
@@ -887,7 +887,7 @@ Chardev *qemu_chr_new_from_opts(QemuOpts *opts,
         return NULL;
     }
 
-    for (i = 0; i < ARRAY_SIZE(chardev_alias_table); i++) {
+    for (i = 0; i < (int)ARRAY_SIZE(chardev_alias_table); i++) {
         if (g_strcmp0(chardev_alias_table[i].alias, name) == 0) {
             name = chardev_alias_table[i].typename;
             break;