cifs: fix noserverino handling when unix extensions are enabled

The uniqueid field sent by the server when unix extensions are enabled
is currently used sometimes when it shouldn't be. The readdir codepath
is correct, but most others are not. Fix it.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>