buildroot

package/targetcli-fb: update URL to the open-iscsi organization

Also add a comment to indicate that python-rtslib-fb and
python-configshell-fb should be bumped every time targetcli-fb is bumped
because upstream usually upgrades all of these packages at the same
time.

Signed-off-by: Christophe Vu-Brugier <cvubrugier@fastmail.fm>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>