virtfs-proxy-helper: Make the helper_opts[] array const

Reduce a bit the memory footprint by making the helper_opts[]
array const.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Acked-by: Greg Kurz <groug@kaod.org>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Message-Id: <20200305010446.17029-4-philmd@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

fsdev/virtfs-proxy-helper.c

@@ -43,7 +43,7 @@
 #define BTRFS_SUPER_MAGIC 0x9123683E
 #endif
 
-static struct option helper_opts[] = {
+static const struct option helper_opts[] = {
     {"fd", required_argument, NULL, 'f'},
     {"path", required_argument, NULL, 'p'},
     {"nodaemon", no_argument, NULL, 'n'},