Bluetooth: Mesh: Remove krp param check

param can never be NULL, so this check is redundant. Coverity complains
about this, as the param variable is accessed before the check, which
would be wrong if param could be NULL.

Fixes #37948.

Signed-off-by: Trond Einar Snekvik <Trond.Einar.Snekvik@nordicsemi.no>