platform/x86: ISST: Add missing write block check

platform/x86: ISST: Add missing write block check

If writes are blocked, then return error during SST-CP enable command.
Add missing write block check in this code path.

Fixes: 8bed9ff7dbcc ("platform/x86: ISST: Process read/write blocked feature status")
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260107060256.1634188-2-srinivas.pandruvada@linux.intel.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>