fs/cifs: keep guid when assigning fid to fileinfo

commit 94f873717571c759b7928399cbbddfa3d569bd01 upstream.

When we open a durable handle we give a Globally Unique
Identifier (GUID) to the server which we must keep for later reference
e.g. when reopening persistent handles on reconnection.

Without this the GUID generated for a new persistent handle was lost and
16 zero bytes were used instead on re-opening.

Signed-off-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <smfrench@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>