package/matchbox: point to new home

The new home of the matchbox project is with the Yocto project.
The old home was already redirecting to it anyway, but better point
directly to the official location.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>