manifest: mcuboot upgrade

MCUboot was synchronized with the upstream SHA:
a9c6d8495e4dbe7d02edf14bb8a9fa1d4e955c0

This version is post MCUboot v1.8.0 version.
It contain a few small fixes more than mentioned release.

Signed-off-by: Andrzej Puzdrowski <andrzej.puzdrowski@nordicsemi.no>
1 file changed