[CIFS] fix saving of resume key before CIFSFindNext

We recently fixed the cifs readdir code so that it saves the resume key
before calling CIFSFindNext. Unfortunately, this assumes that we have
just done a CIFSFindFirst (or FindNext) and have resume info to save.
This isn't necessarily the case. Fix the code to save resume info if we
had to reinitiate the search, and after a FindNext.

This fixes connectathon basic test6 against NetApp filers.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
CC: Stable <stable@kernel.org>
Signed-off-by: Steve French <sfrench@us.ibm.com>