BugLink: http://bugs.launchpad.net/bugs/1670508

Fix memory leaks introduced by the patch
fs/cifs: make share unaccessible at root level mountable

Also move allocation of cifs_sb->prepath to cifs_setup_cifs_sb().
Signed-off-by: Sachin Prabhu <sprabhu@redhat.com>
Tested-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <smfrench@gmail.com>
(cherry picked from commit 4214ebf4)
Signed-off-by: Joseph Salisbury <joseph.salisbury@canonical.com>