Fix the return values of the aarch64 unroll8_eor_aes_gcm_*_*_kernel functions

Fix the return values of the aarch64 unroll8_eor_aes_gcm_*_*_kernel functions

These aren't currently checked when they are called in cipher_aes_gcm_hw_armv8.inc,
but they are declared as returning as size_t the number of bytes they have processed,
and the aes_gcm_*_*_kernel (unroll by 4) versions of these do return the correct
values.

Change-Id: Ic3eaf139e36e29e8779b5bd8b867c08fde37a337

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/20191)