Have nfs ->d_revalidate() report errors properly

	If nfs atomic open implementation ends up doing open request from
->d_revalidate() codepath and gets an error from server, return that error
to caller explicitly and don't bother with lookup_instantiate_filp() at all.
->d_revalidate() can return an error itself just fine...

See
	http://bugzilla.kernel.org/show_bug.cgi?id=15674
	http://marc.info/?l=linux-kernel&m=126988782722711&w=2



for original report.

Reported-by: Daniel J Blueman <daniel.blueman@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>