Make multi-part PAKE operations thread-safe

The only interaction with key IDs here is in the changed function.

Simultaneous API calls on the same operation object are not thread-safe.

Signed-off-by: Ryan Everett <ryan.everett@arm.com>

library/psa_crypto.c

@@ -7953,7 +7953,7 @@ exit:
     if (status != PSA_SUCCESS) {
         psa_pake_abort(operation);
     }
-    unlock_status = psa_unregister_read(slot);
+    unlock_status = psa_unregister_read_under_mutex(slot);
     return (status == PSA_SUCCESS) ? unlock_status : status;
 }