FROMLIST: crypto: x86/poly1305 - add back a needed assignment

One of the assignments that was removed by commit 4a0c1de6 ("crypto:
x86/poly1305 - Remove assignments with no effect") is actually needed,
since it affects the return value.

This fixes the following crypto self-test failure:

    alg: shash: poly1305-simd test failed (wrong result) on test vector 2, cfg="init+update+final aligned buffer"

Bug: 171770067
Link: https://lore.kernel.org/r/20201027080745.GA31045@infradead.org


Fixes: 4a0c1de6 ("crypto: x86/poly1305 - Remove assignments with no effect")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: Ifd01e3694adb618091fa1c1646d677a93382152b