tee: fix possible error pointer ctx dereferencing

Add check for valid ctx pointer and then only dereference ctx to
configure supp_nowait flag.

Fixes: 42bf4152 ("tee: add supp_nowait flag in tee_context struct")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

drivers/tee/tee_core.c

@@ -993,7 +993,9 @@ tee_client_open_context(struct tee_context *start,
 	 * tee_client_open_session() if any in kernel client requires
 	 * different behaviour.
 	 */
-	ctx->supp_nowait = true;
+	if (!IS_ERR(ctx))
+		ctx->supp_nowait = true;
+
 	return ctx;
 }
 EXPORT_SYMBOL_GPL(tee_client_open_context);