DOC: config: Fix typo in ssl_fc_unique_id description

DOC: config: Fix typo in ssl_fc_unique_id description

In ssl_fc_unique_id decription, threre is a reference to the wrong sample
fetch. ssl_bc_unique_id is used instead of ssl_fc_unique_id.

This patch should fix the issue #1449. It may be backported to all
supportted versions.

(cherry picked from commit 15ae22c02cff36579be13c40bac1c37acc60d352)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit c5de4193c42e17db1044197eaf4c46b35eceb3d6)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>