For multipart encrpytion, call psa_cipher_finish(). This is not actually
necessary for non-pathological implementations of ECB (the only currently
supported IV-less cipher algorithm) because it requires the input to be a
whole number of blocks and non-pathological implementations emit the output
block from update() as soon as an input block is available. But in principle
a driver could delay output and thus require a call to finish().
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>