tee: optee: fix uuid comparisons on service discovery

When comparing UUIDs for discovered services we only compare up to the
ptr size instead of the entire UUID

Fixes: 94ccfb78 ("drivers: tee: optee: discover OP-TEE services")
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Etienne Carriere <etienne.carriere@linaro.org>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>