package/fastd: do not overwrite the cmake module path

package/fastd: do not overwrite the cmake module path

fastd's CMakeList.txt completely overwrites CMAKE_MODULE_PATH with its
own, thus causing cmake to not find our own custom one.

We fix fastd by appending its custom value, rather than replacing.

Fixes:

   http://autobuild.buildroot.net/results/69f/69fb2e3b549a069e2898506db918423e6742c589/

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Alexander Dahl <post@lespocky.de>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Baruch Siach <baruch@tkos.co.il>
Cc: Ben Boeckel <mathstuf@gmail.com>
Cc: Jörg Krause <joerg.krause@embedded.rocks>
Cc: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Cc: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>