west.yml: Update mcumgr revision

The update includes support for the
  CONFIG_IMG_MGMT_REJECT_DIRECT_XIP_MISMATCHED_SLOT
Kconfig options that enables mcumgr to check uploaded image for correct
base addres of Direct-XIP application, and rejecting upload if
the upload would not be able to boot from offered slot.

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