west.yml: Update mcumgr revision

Commits affecting Zephyr that are included with the new revision:
    edb485c samples/smp_svr/zephyr: Increase main stack size;
    c0cb989 zephyr: Do not use CONFIG_IMG_MGMT_UPDATABLE_IMAGE_NUMBER
            directly;
    10cda4e zephyr: Fix assert when image number out of range;
    347a418 zephyr: Fix erase command failing for multi-image
            configuration;
    e06e772 zephyr: Fix possible memory leak in
            img_mgmt_impl_write_image_data;
    345caab img_mgmt: fix callback parameter values.

Signed-off-by: Dominik Ermel <dominik.ermel@nordicsemi.no>