staging: lustre: fix build error in errno.c

Turns out we need some more .h files to build properly on all arches.
Specifically errno.h for this file.
Reported-by: kbuild test robot <lkp@intel.com>
Fixes: 0922c008 ("staging: lustre: remove libcfs_all from ptlrpc")
Cc: NeilBrown <neilb@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/ptlrpc/errno.c

@@ -26,6 +26,7 @@
  * Copyright (c) 2013, Intel Corporation.
  */
 
+#include <linux/errno.h>
 #include <lustre_errno.h>
 
 /*