tee: optee: do not check memref size on return from Secure World

Commit c650b8dc ("tee: optee: do not check memref size on return
from Secure World") was mistakenly lost in commit 4602c584 ("optee:
refactor driver with internal callbacks"). Remove the unwanted code
again.

Fixes: 4602c584 ("optee: refactor driver with internal callbacks")
Signed-off-by: Jerome Forissier <jerome@forissier.org>
Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>