smbd: Simplify chroot option in smbd

smbd: Simplify chroot option in smbd

rpmlint has a check for this and prefers to call chdir() before
chroot(). If not it will complain with
missing-call-to-chdir-with-chroot. The old code equivalent secure. See

    http://unixwiz.net/techtips/chroot-practices.html

This removes several unneeded talloc_tos() calls.

Signed-off-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Sat Feb 13 03:50:54 CET 2016 on sn-devel-144