The SIMD based GHASH implementation for arm64 is typically much faster
than the generic one, and doesn't use any lookup tables, so it is
clearly preferred when available. So bump the priority to reflect that.

Fixes: 5a22b198 ("crypto: arm64/ghash - register PMULL variants ...")
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>