arm64/crypto: fix data corruption bug in GHASH algorithm

This fixes a bug in the GHASH algorithm resulting in the calculated hash to be
incorrect if the input is presented in chunks whose size is not a multiple of
16 bytes.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Fixes: fdd23894

 ("arm64/crypto: GHASH secure hash using ARMv8 Crypto Extensions")
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>