[CIFS] relinquish fscache cookie before freeing CIFSTconInfo

Doh, fix a use after free bug.

Signed-off-by: Suresh Jayaraman <sjayaraman@suse.de>
Reviewed-and-Tested-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>