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>