migration: qemu_file_total_transferred() function is monotonic

So delta_bytes can only be greater or equal to zero.  Never negative.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20230504113841.23130-3-quintela@redhat.com>

migration/block.c

@@ -801,13 +801,7 @@ static int block_save_iterate(QEMUFile *f, void *opaque)
 
     qemu_put_be64(f, BLK_MIG_FLAG_EOS);
     delta_bytes = qemu_file_total_transferred(f) - last_bytes;
-    if (delta_bytes > 0) {
-        return 1;
-    } else if (delta_bytes < 0) {
-        return -1;
-    } else {
-        return 0;
-    }
+    return (delta_bytes > 0);
 }
 
 /* Called with iothread lock taken.  */