Recent changes in NFSd cause a directory which is mounted-on
to not appear properly when the filesystem containing it is exported.

*exp_get* now returns -ENOENT rather than NULL and when
  commit 5d3dbbea
removed the NULL checks, it didn't add a check for -ENOENT.
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>