cifs: fix error handling in mount-time DFS referral chasing code

cifs: fix error handling in mount-time DFS referral chasing code

commit 7b91e2661addd8e2419cb45f6a322aa5dab9bcee upstream.

If the referral is malformed or the hostname can't be resolved, then
the current code generates an oops. Fix it to handle these errors
gracefully.

Reported-by: Sandro Mathys <sm@sandro-mathys.ch>
Acked-by: Igor Mammedov <niallain@gmail.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>