Use latest version of afb-helpers submodule.

Changes of afb-helpers:

(52f0478 - Jonathan Aillet) Remove unnecessary 'AFB_DEBUG' redefinition
(fc1c62a - Jonathan Aillet) Use binding version to handle dynapi
(5811a53 - Jonathan Aillet) At search, use the prefix parameter as a prefix
(2c29f15 - Loïc Collignon) Remove deprecated use of cmake/Qt macro
(5bec8c5 - Loïc Collignon) Rename method to avoid conflict with Qt's one

Change-Id: Ief77446c27e4c6299c1ba3e82d42a35ecf798e7f
Signed-off-by: Loïc Collignon <loic.collignon@iot.bzh>