block/sheepdog: Replace magic val by NANOSECONDS_PER_SECOND definition

Use self-explicit NANOSECONDS_PER_SECOND definition instead
of magic value.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200921110145.520944-1-philmd@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/sheepdog.c

@@ -740,7 +740,7 @@ static coroutine_fn void reconnect_to_sdog(void *opaque)
         if (s->fd < 0) {
             trace_sheepdog_reconnect_to_sdog();
             error_report_err(local_err);
-            qemu_co_sleep_ns(QEMU_CLOCK_REALTIME, 1000000000ULL);
+            qemu_co_sleep_ns(QEMU_CLOCK_REALTIME, NANOSECONDS_PER_SECOND);
         }
     };