chardev: Indent list of chardevs

Following the example of qemu_opts_print_help(), indent all entries in
the list of character devices.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

chardev/char.c

@@ -572,7 +572,7 @@ help_string_append(const char *name, void *opaque)
 {
     GString *str = opaque;
 
-    g_string_append_printf(str, "\n%s", name);
+    g_string_append_printf(str, "\n  %s", name);
 }
 
 static const char *chardev_alias_translate(const char *name)