crypto: arm64/aes-gcm-ce - fix scatterwalk API violation

Commit 71e52c27 ("crypto: arm64/aes-ce-gcm - operate on
two input blocks at a time") modified the granularity at which
the AES/GCM code processes its input to allow subsequent changes
to be applied that improve performance by using aggregation to
process multiple input blocks at once.

For this reason, it doubled the algorithm's 'chunksize' property
to 2 x AES_BLOCK_SIZE, but retained the non-SIMD fallback path that
processes a single block at a time. In some cases, this violates the
skcipher scatterwalk API, by calling skcipher_walk_done() with a
non-zero residue value for a chunk that is expected to be handled
in its entirety. This results in a WARN_ON() to be hit by the TLS
self test code, but is likely to break other user cases as well.
Unfortunately, none of the current test cases exercises this exact
code path at the moment.

Fixes: 71e52c27 ("crypto: arm64/aes-ce-gcm - operate on two ...")
Reported-by: Vakul Garg <vakul.garg@nxp.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Vakul Garg <vakul.garg@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>