platform/x86: ISST: Correct locked bit width

SST-PP locked bit width is set to three bits. It should be only one bit.
Use SST_PP_LOCK_WIDTH define instead of SST_PP_LEVEL_WIDTH.

Fixes: ea009e4769fa ("platform/x86: ISST: Add SST-PP support via TPMI")
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260323153635.3263828-1-srinivas.pandruvada@linux.intel.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>